If f(x) = 4 – x2 and g(x) = 6x, which expression is equivalent to (g – f)(3)?

F(x) = 4 - x²    Df: x∈R

g(x) = 6x  Dg: x∈R

Df = Dg therefore (g - f)(x) = g(x) - f(x)

(g - f)(3) = g(3) - f(3)

subtitute the value of x to equations:

g(3) = 6 · 3 = 18
f(3) = 4 - 3² = 4 - 9 = -5

(g - f)(3) = 18 - (-5) = 18 + 5 = 23