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

Question

Philoid · Accepted 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)]