Question

If f(x) = ax² + 6x + 5 attains its maximum value at x = 1, then the value of a is

Options

• 0

• 5

• 3

• –3

Answer 1

–3

Explanation:

f(x) = ax² + 6x + 5

f'(x) = 2ax + 6

Since f(x) is maximum at x = 1.

∴ f'(1) = 2a(1) + 6 = 0 ⇒ a = –3.