Q. 374.3( 3 Votes )

There are two values of a which makes determinant, ,then sum of these number is
A. 4

B. 5

C. -4

D. 9

Answer :

Given



= 1 [2a2 – (-4)] + 2 [4a – 0] + 5 [8 – 0] = 86


= 1 [2a2 + 4] + 2 [4a] + 5 [8] = 86


= 2a2 + 4 + 8a + 40 = 86


= 2a2 + 8a + 44 = 86


= 2a2 + 8a = 42


= 2 (a2 + 4a) = 42


= (a2 + 4a) = 21


a2 + 4a – 21 = 0


(a + 7) (a – 3) = 0


a = -7 or 3


Sum of these numbers is -7 + 3 = -4. [Option (C)]

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