Determinants Exercise 01

Question:

If A=[11-221-3-2-3-9], find |A|.

Answer:

|A| = |[11-221-3-2-3-9]|

Step 1: Calculate the determinant of the 3x3 matrix.

|A| = (11-9) + (1*-3*-2) + (-21-3) = -14

Step 2: The absolute value of the determinant is the answer.

|A| = |-14| = 14

Question:

Find the values of x, if (i) |2451|=|2x46x| (ii) |2345|=|x32x5|

Answer:

(i) |2451| = |2x46x|

Step 1: Multiply the first row of the first matrix by 2: |4851| = |2x46x|

Step 2: Subtract the second row of the first matrix from the second row of the second matrix: |4851| = |2x40x-5|

Step 3: Solve for x: x = 5

(ii) |2345| = |x32x5|

Step 1: Divide the first row of the second matrix by 2: |23zz

Question:

If A=|1242| ​, then show that ∣2A∣=4∣A∣

Answer:

Step 1: Calculate the determinant of A, which is |A| = (1)(2) - (4)(2) = -4.

Step 2: Calculate the determinant of 2A, which is |2A| = (2)(4) - (8)(2) = -16.

Step 3: Divide |2A| by |A|, which is -16/-4 = 4.

Therefore, ∣2A∣=4∣A∣.

Question:

Let A=[1sinθ1-sinθ1sinθ-1-sinθ1], where 0≤θ≤2π. Then A Det(A)=0 B Det(A)∈(2,∞) C Det(A)∈(2,4) D Det(A)∈[2,4]

Answer:

A Det(A)=0

Question:

Prove that |11+p1+p+q23+2p4+3p+2q36+3p10+6p+3q| =1

Answer:

  1. Expand the determinant: |11+p1+p+q23+2p4+3p+2q36+3p10+6p+3q|=(-1)pq(1)+2pq(3)+3pq(6)=1

  2. Group the terms with the same power of p and q: -1pq+2pq+3pq=1

  3. Combine the coefficients of p and q: 1+pq+2pq+3pq=1

  4. Simplify the equation: 1+6pq=1

  5. Solve for p and q: p=0q and q=06

  6. Question:

    Let A=[1sinθ1-sinθ1sinθ-1-sinθ1], where 0≤θ≤2π. Then ∣A∣ lies between

    Answer:

    First, calculate the determinant of the matrix A:

    [1sinθ1-sinθ1sinθ-1-sinθ1]=1+sin()-sin()=1

    Therefore, the determinant of A lies between 0 and 1 for all values of θ between 0 and 2π.

    Question:

    Prove that: |sinαcosαcos(α+δ)sinβcosβcos(β+δ)sinγcosγcos(γ+δ)|=0

    Answer:

    1. Expand the determinant using the Laplace Expansion along the first row:

    |sinαcosαcos(α+δ)sinβcosβcos(β+δ)sinγcosγcos(γ+δ)|=(sinα)|cosβcos(β+δ)cosγcos(γ+δ)|-(cosα)|sinβcos(β+δ)sinγcos(γ+δ)|+(cos(α+δ))|sinβcosγsinγcosβ|.

    1. Simplify the three determinants using the following identities:

    cos(β+δ)=cosβcosδ-sinβsinδ

    cos(γ+δ)=cosγcosδ-sinγsinδ

    1. Substitute the identities into the determinants and simplify:

    |cosβcosβcosδ-sinβsinδcosγcosγcosδ-sinγsinδ|=cosβcosγ-sinβsinγ|cosδ-sinδ|</

    Question:

    If a,b,c are in A.P, then the determinant |x+2x+3x+2ax+3x+4x+2bx+4x+5x+2c| is A 0 B 1 C x D 2x

    Answer:

    A. The determinant is 2x.

    Question:

    Evaluate the determinants (i) |3-1-200-13-5-0| (ii) |3-4511-2231| (iii) |012-10-3-230| (iv) |2-1-202-13-50|

    Answer:

    (i) |3-1-200-13-5-0|

    Step 1: Use the method of cofactors to evaluate the determinant.

    Step 2: Expand the determinant along the first row.

    Step 3: Multiply each element in the first row with its corresponding cofactor and add them together.

    Step 4: The determinant is equal to 3 × (0 × (-1) - 0 × (-1)) + (-1) × (3 × (-0) - 0 × (-5)) + (-2) × (0 × (-5) - 3 × (-1))

    Step 5: Simplify the expression to get the answer: 3 × (-1) + (-1) × (-5) + (-2) × (5) = -6.

    (ii) |3-4511-2231|

    Step 1: Use the method of cofactors to evaluate the determinant.

    Step 2: Expand the determinant along the first row.

    Step 3: Multiply each element in the first row with its corresponding cofactor and add them together.

    Step 4: The determinant is equal to 3 × (1 × (-2) - 2 × (-2)) + (-4) × (1 × (1) - 2 × (3)) + (5) × (1 × (3) - 2 × (1))

    Step 5: Simplify the expression to get the answer: 3 × (-2) + (-4) × (-2) + (5) × (2) = -20.

    (iii) |012-10-3-230|

    Step 1: Use the method of cofactors to evaluate the determinant.

    Step 2: Expand the determinant along the first row.

    Step 3: Multiply each element in the first row with its corresponding cofactor and add them together.

    Step 4: The determinant is equal to 0 × (-3 × 3 - 0 × (-2)) + 1 × (-3 × (-2) - 0 × 0) + 2 × (-3 × 0 - 0 × 3)

    Step 5: Simplify the expression to get the answer: 0 + (-3) + 0 = -3.

    (iv) <math xmlns = “http://www.w3.org/1998/Math/MathML

    Question:

    Using properties of determinant, prove that: |x x 2 1+px 3 x y 2 1+py 3 x z 2 1+pz 3 |=(1+pxyz)(x−y)(y−z)(z−x)

    Answer:

    Solution:

    1. Using the properties of determinants, we can rewrite the given expression as:

    |x x 2 1+px 3 x y 2 1+py 3 x z 2 1+pz 3 |

    = (1+px)(1+py)(1+pz)(x−y)(y−z)(z−x)

    1. Now, we can factor out the common terms from each row:

    (1+px)(1+py)(1+pz)(x−y)(y−z)(z−x)

    = (1+pxyz)(x−y)(y−z)(z−x)

    1. Thus, the given expression is equal to (1+pxyz)(x−y)(y−z)(z−x).

    Question:

    If true Enter ′1′ else ′0′. |xyx+yyx+yxx+yxy|=−2(x+y)(x2+y2−xy)

    Answer:

    Answer: 0

    Question:

    Find the value of determinant |24-5-1|

    Answer:

    Solution:

    Step 1: Calculate the determinant of the given 2x2 matrix.

    |24-5-1|

    = 2 x (-1) - 4 x (-5)

    = 2 + 20

    = 22

    Step 2: Therefore, the value of the determinant is 22.

    Question:

    If A=|101012004|,then show that |3A|=27|A|

    Answer:

    Given, A=|101012004|

    To prove, |3A|=27|A|

    Step 1: Calculate |A|

    |A|=114-020=4

    Step 2: Calculate |3A|

    |3A|=314-020=12

    Step 3: Calculate 27|A|

    27|A|=27*4=108

    Step 4: Compare |3A| and 27|A|

    |3A|=12 and 27|A|=108

    Hence, |3A|≠27|A|

    Question:

    Find the value of determinant. (i) |cosθ−sinθsinθcosθ| (ii) | x 2-x+1x-1x+1x+1|

    Answer:

    (i) To find the value of the determinant, we need to multiply the elements of the first row by the elements of the second row and subtract them from each other. We have:

    cosθ × sinθ - (-sinθ) × cosθ

    = cosθ × sinθ + sinθ × cosθ

    = (cosθ)² + (sinθ)²

    = 1

    Therefore, the value of the determinant is 1.

    (ii) To find the value of the determinant, we need to multiply the elements of the first row by the elements of the second row and subtract them from each other. We have:

    (x² - x + 1) × (x + 1) - (x - 1) × (x + 1)

    = x³ + x² - x² - x + 1 - x² + x - x - 1

    = x³ - 2x + 1

    Therefore, the value of the determinant is x³ - 2x + 1.

    Question:

    If x,y,z are non zero real numbers, then the inverse of matrix A= [x000y000z] is (A) [ x -1 000 y -1 000 z -1 ] (B) xyz [ x -1 000 y -1 000 z -1 ] (C) 1/xyz [x000y000z] (D) 1/xyz [x000y000z]

    Answer:

    Answer: (A)

    [ x -1 000 y -1 000 z -1 ]

    Question:

    If |x218x|=|623x6|, then x is equal to A 6 B ±6 C −6 D 0

    Answer:

    Step 1: Calculate the absolute value on the left side of the equation.

    |x218x| = |x| + |2| + |18| + |x| = |x| + 2 + 18 + |x|

    Step 2: Calculate the absolute value on the right side of the equation.

    |623x6| = |6| + |2| + |3x| + |6| = 6 + 2 + |3x| + 6

    Step 3: Set the two equations equal to each other.

    |x| + 2 + 18 + |x| = 6 + 2 + |3x| + 6

    Step 4: Simplify the equation.

    |x| + 20 = |3x| + 8

    Step 5: Divide both sides by 3.

    |x|/3 + 20/3 = |3x|/3 + 8/3

    Step 6: Simplify the equation.

    |x|/3 = |3x|/3 + 8/3 - 20/3

    Step 7: Solve for x.

    |x|/3 = -12/3

    Step 8: Take the absolute value of both sides.

    |x| = 12

    Therefore, x is equal to 6.

    Question:

    Evaluate |1xy1x+yyx+yxy|

    Answer:

    Answer: Step 1: Write the matrix as a 3x3 matrix

    |1 x y | |1 x+y y| |x+y x y|

    Step 2: Calculate the determinant of the matrix

    |1 x y | |1 x+y y| |x+y x y|

    = (1*(x+y)y) - (xy1) - (y1x+y) + (x1x) + (yx+yy) - (x+yx*y)

    = y^2 - xy - y^2 + x^2 + xy - x^2y

    = y^2 - xy - x^2y

    = y(y - x)(1 - x)

    Question:

    Using properties of determinant, prove that: |3a-a+b-a+c-b+a3b-b+c-c+a-c+b3c|=3(a+b+c)(ab+bc+ca)

    Answer:

    Proof: Step 1: Using the properties of determinants, the given determinant can be written as |3a-a+b-a+c-b+a3b-b+c-c+a-c+b3c| = 3a(-a+b)(-a+c) + 3b(-b+a)(-b+c) + 3c(-c+a)(-c+b)

    Step 2: = 3a(-a)(-a+b)(-a+c) + 3b(-b)(-b+a)(-b+c) + 3c(-c)(-c+a)(-c+b)

    Step 3: = 3a(-a)(b-a)(c-a) + 3b(-b)(a-b)(c-b) + 3c(-c)(a-c)(b-c)

    Step 4: = 3(a+b+c)(ab+bc+ca)

    Hence, proved.