find f ′(a) at the given number a. f(x) = sqrt(5x + 5), a = 4

Answer 1

f(x) = sqrt 5 * (x+1)^0.5
f'(x) = sqrt 5 * 0.5(x+1)^-0.5
f'(4) = 5^0.5 * 0.5 * 5^- 0.5 = 0.5

Answer 2

f(x) = sqrt(5x+5)
f(a) = sqrt(5a+5)
f'(a) = 5/[2sqrt(5a+5)]
f'(4) = 5/[2sqrt(5(4)+5)]
f'(4) = 5/[2sqrt(20+5)]
f'(4) = 5/[2sqrt(25)]
f'(4) = 5/[2(5)]
f'(4) = 5/10
f'(4) = 1/2