Let M = A = a b c d : a , b , c , d ∈ ± 3 , ± 2 , ± 1 , 0 . Define f : M → Z , as…

Let M=A=abcd:a,b,c,d±3,±2,±1,0. Define f:MZ, as fA=detA, for all AM where Z is set of all integers. Then the number of AM such that fA=15 is equal to                 .

Solution

.A=ad-bc=15

where a,b,c,d±3,±2,±1,0

Case I: ad=9 & bc=-6

For ad possible pairs are 3,3,-3,-3. 

For bc possible pairs are 3,-2,-3,2,-2,3,2,-3 

So, total number of matrices in case I=2×4=8

Case II: ad=6 & bc=-9

Similarly, total number of matrices in case II =2×4=8

Hence, total number of matrices are 16.

Asked in: JEE Main 2021 (25 Jul Shift 1)

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