Find:(f*g)(3)....

Question

Given: f(x )=2x^2 +3x – 5, g (x )=x +9. Find:(f*g)(3)

Answer 1

You can either multiply the two functions together and then plug in 3, our you can plug in 3 to each one and multiply the results together.

Method 1 (multiply functions together)

(2x² + 3x - 5)(x + 9) = 2x³ + 21x² + 22x - 45 and plugging in 3 gives: 2(3)³ + 21(3)² + 22(3) - 45 = 264

Method 2 (plug in 3 to each and then multiply the results)

f(3) = 2(3)² + 3(3) - 5 = 22

g(3) = (3) + 9 = 12

22•12 = 264