Question

If f(x) = ax + b, a and b are positive real numbers and if f(f(x)) = 9x + 8, then the value of a + b is:
(1) 3
(2) 4
(3) 5
(4) 6​

Answer 1

Answer:

5

Step-by-step explanation:

• f(f(x))=a(ax+b)+b
• 9x+8=aax+ab+b
• a^2=9
• a=3
• ab+b=8
• 3b+b=8
• 4b=8
• b=2
• so, a+b=3+2=5