Question

If f(x) = kx² + 7x – 4 and f′(5) = 97 then what is the value of k?

Options

• –4

• 0

• 4

• 9

Answer 1

9

Explanation:

Given: f(x) = kx² + 7x – 4

Differentiate with respect to x:

f′(x) = 2kx + 7

Now use f′(5) = 97

2k(5) + 7 = 97

10k = 97 – 7

10k = 90

k = `90/10`

k = 9