Question

If xy = c2, then the minimum value of ax + by is

(A) c√(ab)

(B) 2c√(ab)

(C) -c√(ab)

(D) -2c√(ab)

Answer 1

Answer is (B) 2c√(ab)

We have

Differentiating w.r.t. x, we get

At x = +c√(b/a), ax + by will be minimum.

The minimum value is