knowledge-route Maths10 Cha7


title: “Lata knowledge-route-Class10-Math1-2 Merged.Pdf(1)” type: “reveal” weight: 1

ARITHMATIC PROGRESSIONS

ARITHMATIC PROGRESSIONS

6.1 PROGRESSIONS : Those sequence whose terms follow certain patterns are called progression. Generally there are three types of progression.

(i) Arithmetic Progression (A.P.)

(ii) Geometric Progression (G.P.)

(iii) Harmonic Progression (H.P.)

ARITHMATIC PROGRESSIONS

6.2 ARTHMETIC PROGRESSION :

A sequence is called an A.P., if the difference of a term and the previous term is always same. i.e. d=tn+1 - tn= Constant for all nN. The constant difference, generally denoted by ’ d ’ is called the common difference.

ARITHMATIC PROGRESSIONS

Ex. 1 Find the common difference of the following A.P. : 1,4,7,10,13,16 ……

ARITHMATIC PROGRESSIONS

Sol. 41=74=107=1310=1613=3 (constant). Common difference (d)=3.

ARITHMATIC PROGRESSIONS

6.3 GENERAL FORM OF AN A.P.:

If we denote the starting number i.e. the 1st  number by ’ a ’ and a fixed number to the added is ’ d ’ then a, a +d,a+2d,a+3d,a+4d forms an A.P.

ARITHMATIC PROGRESSIONS

Ex. 2 Find the A.P. whose 1st  term is 10 & common difference is 5.

ARITHMATIC PROGRESSIONS

Sol. Given : First term (a)=10 & Common difference (d)=5. A.P. is 10,15,20,25,30,..

ARITHMATIC PROGRESSIONS

6.4 nth  TERM OF AN A.P.:

Let A.P. be a,a+d,a+2d,a+3d,..

Then, First term (a1)=a+0.d

Second term (a2)=a+1.d

Third term (a3)=a+2.d

nth  term (an)=a+(n1)d

an=a+(n1)d is called the nth  term.

ARITHMATIC PROGRESSIONS

Ex. 3 Determine the A.P. whose their term is 16 and the difference of 5th  term from 7th  term is 12.

ARITHMATIC PROGRESSIONS

Sol. Given: a3=a+(31)d=a+2d=16

a7a5=12

(a+6d)(a+4d)=12

a+6da4d=12

2d=12

a=1612

Put d=6 in equation (i)

a=4 A.P. is 4,10,16,22,28,.

ARITHMATIC PROGRESSIONS

Ex. 4 Which term of the sequence 72, 70, 68, 66, ….. is 40 ?

ARITHMATIC PROGRESSIONS

Sol. Here 1st  term x=72 and common difference d=7072=2

For finding the value of n

an=a+(n1)d

40=72+(n1)(2)

4072=2n+2

32=2n+2

34=2n

n=17

17th  term is 40 .

ARITHMATIC PROGRESSIONS

Ex. 5 Is 184, a term of the sequence 3,7,11,…. ?

ARITHMATIC PROGRESSIONS

Sol. Here 1st  term (a)=3 and common difference (d)=73=4 nth  term (an)=a+(n1)d

184=3+(n1)4181=4n4185=4n

n=1854 Since, n is not a natural number.

184 is not a term of the given sequence.

ARITHMATIC PROGRESSIONS

Ex. 6 Which term of the sequence 20, 1912,1812,1734 is the 1 st negative term.

ARITHMATIC PROGRESSIONS

Sol. Here 1st  term (a)=20, common difference (d)=191420=34

Let nth  term of the given A.P. be 1st  negative term an<0

i.e. a+(n1)d<0

20+(n1)(34)<08343n4<03n>83n>833n>2723

Since, 28 is the natural number just greater then 2723.

1st  negative term is 28th .

ARITHMATIC PROGRESSIONS

Ex. 7 If pth ,qth  and rth  term of an A.P. are a,b,c respectively, then show than a(qr)+b(p)+c(pq)=0.

ARITHMATIC PROGRESSIONS

Sol. ap=aA+(p1)D=a

aq=b

A+(q1)D=b

ar=c

A+(r+1)D=c

Now, L.H.S.

=a(qr)+b(rp)+c(pq)

=A+(p1)D(qr)+A+(q1)D(rp)+A+(r1)D(pq)

=0. R.H.S

ARITHMATIC PROGRESSIONS

Ex. 8 If m times the mth  term of an A.P. is equal to n times its th term. Show that the (m+n)th term of the A.P.

ARITHMATIC PROGRESSIONS

Sol. Let A the 1st  term and D be the common difference of the given A.P.

Then, mam=nan

m[A+(m1)D]=n[A+(n1)D]

A(m1)+D[m+n(mn)(mn)]=0am+n=0

A+(m+n1)D=0

ARITHMATIC PROGRESSIONS

Ex. 9 If the pth  term of an A.P. is q and the qth  term is p, prove that itsth  term is (p+qn).

ARITHMATIC PROGRESSIONS

Sol. ap=qA+(p1)D=q

& aq=pA+(q1)D=p

Solve (i) & (ii) to get D=1 & A=p+q1

an=A+(n1)D

an=(p+q1)+(n1)(1)an=p+qn.

ARITHMATIC PROGRESSIONS

Ex. 10 If the mth  term of an A.P. 1n and nth  term be 1m then show that its (mn) term is 1 .

ARITHMATIC PROGRESSIONS

Sol.

am=1nA+(m1)D=1n(i)

am=1mA+(n1)D=1m(ii)

By solving (i) & (ii) D=1mn & A=1mn

amn=A+(mn1)D=1.

ARITHMATIC PROGRESSIONS

6.5 mth  TERM OF AN A.P. FROM THE END :

Let ’ a ’ be the 1st  term and ’ d ’ be the common difference of an A.P. having n terms. Then mth  term from the end is (nm+1)th  term from beginning or n(m)th  term from beginning.

ARITHMATIC PROGRESSIONS

Ex. 11 Find 20th  term from the end of an A.P. 3,7,11….. 407.

ARITHMATIC PROGRESSIONS

Sol. 407=3+(n1)4n=102

20th  term from end m=20

a102(201)=a10219=a83 from the beginning.

a83=3+(83+1)4=331.

ARITHMATIC PROGRESSIONS

6.6 SELECTION OF TERMS IN AN A.P. :

Sometimes we require certain number of terms in A.P. The following ways of selecting terms are generally very convenient.

No. of Terms Terms Common Difference
For 3 terms ad,a,a+d d
For 4 terms a3d,ad,a+d,a+3d 2d
For 5 terms a2d,ad,a,a+d,a+2d d
For 6 terms a5d,a3d,ad,a+d,a+3d,a+5d 2d

ARITHMATIC PROGRESSIONS

Ex. 12 The sum of three number in A.P. is -3 and their product is 8. Find the numbers.

ARITHMATIC PROGRESSIONS

Sol. Three no. ’s in A.P. be ad,a,a+d

ad+a+a+d=33a=3a=1(ad)a(a+d)=8a(a2d2)=8

(1)(1d2)=81d2=8d2=9d=±3

 If a=8andd=3 numbers are 4,1,2. If a=8a=8andd= numbers are 2,1,4

ARITHMATIC PROGRESSIONS

6.7 SUM OF n TERMS OF AN A.P. :

Let A.P. be a,a+d,a+1d,a+3d,...a+(n1)d

Then, Sn=a+(a+d)+..+a+(n2)d+a+(n1)d

also, Sn=a+(n1)d+a+(n2)d++(a+d)+a

Add (i) & (ii)

2Sn=2a+(n1)d+2a+(n1)d++2a+(n1)d

2Sn=n[2a+(n1)d]Sn=n2[2a+(n+1)d]

Sn=n2[a+a+(n1)d]=n2[a+]Sn=n2[a+] where is the last term.

ARITHMATIC PROGRESSIONS

Ex. 13 Find the sum of 20 terms of the A.P. 1,4,7,10…..

ARITHMATIC PROGRESSIONS

Sol. a=1,d=3Sn=n2[2a+(n1)d]S20=202[2(1)+(201)3]

ARITHMATIC PROGRESSIONS

Ex. 14 Find the sum of all three digit natural numbers. Which are divisible by 7.

ARITHMATIC PROGRESSIONS

Sol. 1st  no. is 105 and last no. is 994 .

Find n994=105+(n+1)7

n=128 Sum, S128=1282[105+994]

ARITHMATIC PROGRESSIONS

6.8 PROPERTIES OF A.P. :

(A) For any real numbers a and b, the sequence whose nth  term is an=a+b is always an A.P. with common difference ’ a ’ (i.e. coefficient of term containing n )

(B) If any nth  term of sequence is a linear expression in n then the given sequence is an A.P.

(C) If a constant term is added to or subtracted from each term of an A.P. then the resulting sequence is also an A.P. with the same common difference.

(D) If each term of a given A.P. is multiplied or divided by a non-zero constant K, then the resulting sequence is also an A.P. with common difference Kd or respectively. Where d is the common difference of the given A.P.

(E) In a finite A.P. the sum of the terms equidistant from the beginning and end is always same and is equal to the sum of 1st  and last term.

(F) If three numbers a,b,c are in A.P., then 2b=a+c.

ARITHMATIC PROGRESSIONS

Ex. 15 Check whether an=2n2+1 is an A.p. or not.

ARITHMATIC PROGRESSIONS

Sol. an=2n2+1 Then an+1=2(n+1)2+1

an+1an=2(n2+2n+1)+12n21=2n2+4n+2+12n21=4n+2, which is not constant  The above sequence is not an A.P. 

ARITHMATIC PROGRESSIONS

DAILY PRACTIVE PTOBLEMS 6

OBJECTIVE DPP - 6.1

1. pth  term of the series (31n)+(3+2n)+(33n)+ will be

(A) 3+pn

(B) 3pn

(C) 3+np

(D) 3np

ARITHMATIC PROGRESSIONS

Que. 1
Ans. B

ARITHMATIC PROGRESSIONS

2. 8th  term of the series 22+2+0+ will be

(A) 52

(B) 52

(C) 102

(D) 102

ARITHMATIC PROGRESSIONS

Que. 2
Ans. A

ARITHMATIC PROGRESSIONS

3. If 9th  term of an A.P. be zero then the ratio of its 29th  and 19th  term is

(A) 1:2

(B) 2:1

(C) 1:3

(D) 3:1

ARITHMATIC PROGRESSIONS

Que. 3
Ans. B

ARITHMATIC PROGRESSIONS

4. Which term of the sequence 3,8,13,18,. is 498

(A) 95th 

(B) 100 th

(C) 102th 

(D) 101th 

ARITHMATIC PROGRESSIONS

Que. 4
Ans. B

ARITHMATIC PROGRESSIONS

5. Which of the following sequence is an A.P.

(A) f(n)=ab+bnN

(B) f(n)=krn,nN

(C) f(n)=(an+b)krn,nN

(D) f(n)=1a(n+bn),nN

ARITHMATIC PROGRESSIONS

Que. 5
Ans. A

ARITHMATIC PROGRESSIONS

6. If the nth  term of an A.P. be (2n1) then the sum of its firs n terms will be

(A) n21

(B) (2n1)2

(C) n2

(D) n2+1

ARITHMATIC PROGRESSIONS

Que. 6
Ans. C

ARITHMATIC PROGRESSIONS

7. The interior angles of polygon are in A.P. if the smallest angles be 1200 and the common difference be 5 , then the number of sides is

(A) 8

(B) 10

(C) 9

(D) 6

ARITHMATIC PROGRESSIONS

Que. 7
Ans. C

ARITHMATIC PROGRESSIONS

8. In the first, second and last terms of an A.P. be a,b,2a respectively, then its sum will

(A) aba+b

(B) ab2(ba)

(C) 3ab2(ba)

(D) 3ab4(ba)

ARITHMATIC PROGRESSIONS

Que. 8
Ans. C

ARITHMATIC PROGRESSIONS

SUBJECTIVE DPP - 6.2

1. Is 51 a term of the A.P. 5,8,11,14,.. ?

ARITHMATIC PROGRESSIONS

Sol. 1 No

ARITHMATIC PROGRESSIONS

2. Find the common difference of an A.P. whose first term is 100 and the sum of whose first six terms is five times the sum of the next six terms.

ARITHMATIC PROGRESSIONS

Sol. 2 10

ARITHMATIC PROGRESSIONS

3. Find three number in A.P. whose sum is 21 and their product is 336.

ARITHMATIC PROGRESSIONS

Sol. 3 6,7,8

ARITHMATIC PROGRESSIONS

4. A student purchased a pen for Rs. 100. At the end of 8 years, it was valued at Rs. 20. Assuming the yearly depreciation is constant amount, find the annual depreciation.

ARITHMATIC PROGRESSIONS

Sol. 4 10

ARITHMATIC PROGRESSIONS

5. The fourth term of an A.P. is equal to three times the first term and the seventh term exceeds twice the third by one. Find the first term and the common difference.

ARITHMATIC PROGRESSIONS

Sol. 5 3,2

ARITHMATIC PROGRESSIONS

6. Which term of the sequence 17,1615,1525,1435 is the first negative term.

ARITHMATIC PROGRESSIONS

Sol. 6 23rd

ARITHMATIC PROGRESSIONS

7. If Sn=n2p and Sm=m2p(mn) in an A.P. Prove that Sp=p3.

ARITHMATIC PROGRESSIONS

8. Find the sum of all the three digit numbers which leave remainder 2 when divided by 5 .

ARITHMATIC PROGRESSIONS

Sol. 8 98910

ARITHMATIC PROGRESSIONS

9. Find the sum of all two digit odd positive numbers

ARITHMATIC PROGRESSIONS

Sol. 9 2475

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10. Find the 10th  term from end of the A.P. 4,9,14,….. 254 .

ARITHMATIC PROGRESSIONS

Sol. 10 209

ARITHMATIC PROGRESSIONS

11. 200 logs are stacked in the following manner: 20 logs in the bottom row, 19 in the next row, 18 in the row next to it and so on. In how many rows the 200 logs are placed and how many logs are in the top row ?

ARITHMATIC PROGRESSIONS

Sol. 11 16 rows, 5 logs

ARITHMATIC PROGRESSIONS

12. The sum of the first n term of an A.P. is given by Sn=3n24n. Determine the A.P. and its 12th  term.

[CBSE - 2004]

ARITHMATIC PROGRESSIONS

Sol. 12 1,5,11,..& a12=65

ARITHMATIC PROGRESSIONS

13. Find the sum of the first 25 terms of an A.P. whose nth  term is given by tn=23n

[CBSE - 2004]

ARITHMATIC PROGRESSIONS

Sol. 13 925

ARITHMATIC PROGRESSIONS

14. Find the number of terms of A.P. 54, 54, 48….. so that their sum is 513 .

[CBSE - 2005]

ARITHMATIC PROGRESSIONS

Sol. 14 18,19

ARITHMATIC PROGRESSIONS

15. In an A.P., the sum of first n terms is 3n22+5n2 Find its 25th  term.

[CBSE - 2006]

ARITHMATIC PROGRESSIONS

Sol. 15 76

ARITHMATIC PROGRESSIONS

16. Which term of the arithmetic progression 8,1420,26,…. will be 72 more than its 41st  term ?

[CBSE - 2006]

ARITHMATIC PROGRESSIONS

Sol. 16 53rd

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17. The first term, common difference and last term of an A.P. are 12, 6 and 252 respectively. Find the sum of all terms of this A.P.

[CBSE - 2007]

ARITHMATIC PROGRESSIONS

Sol. 17 5412

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18. Write the next term of the 8,18,32,

[CBSE - 2008]

ARITHMATIC PROGRESSIONS

Sol. 18 50

ARITHMATIC PROGRESSIONS

19. The sum of the 4th  and 8th  terms of an A.P. is 24 and the sum of the 6th  and 10th  terms is 44 . Find the first three terms of the A.P.

[CBSE - 2008]

ARITHMATIC PROGRESSIONS

Sol. 19 13,8,3



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