Question

If x = – 1 and x = 2 are extreme points of the function

y = a log x + bx²+ x, then

• A. a = 2, b =1/2
• B. a = 2, b = – ½
• C. a = –2, b = ½
• D. a = – 2, b = – ½

Answer 1

Answer: (B)

a = 2, b = – ½

Answer 2

$\frac{dy}{dx} = \frac{a}{x}$ + 2bx + 1

since x = – 1, x = 2 are extreme points

so $\frac{dy}{dx}$ = 0

Ž –a – 2b + 1 = 0 & a/2 + 4b + 1 = 0

a + 2b – 1 = 0 & a + 8b + 2 = 0

Ž a = 2 & b = – ½