Matrices and Determinants 1 Question 17

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17. The number of A in Tp such that det(A) is not divisible by p, is

======= Passage II

Let p be an odd prime number and Tp be the following set of 2×2 matrices

Tp=A=[abca];a,b,c0,1,2,,p1

(2010)

####17. The number of A in Tp such that det(A) is not divisible by p, is

3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed

(a) 2p2

(c) p33p

(b) p35p

(d) p3p2

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Answer:

Correct Answer: 17. ( d)

Solution:

  1. The number of matrices for which p does not divide Tr(A)=(p1)p2 of these (p1)2 are such that p divides |A|. The number of matrices for which p divides Tr(A) and p does not divides |A| are (p1)2.

Required number =(p1)p2(p1)2+(p1)2

=p3p2



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