An increasing linear function is of the form y = ax + b where a is positive.

It is given that f(f(x))=4x+3

=> f(ax + b) = 4x + 3

=> a(ax + b) + b = 4x + 3

=> a^2x + ab + b = 4x + 3

=> a^2 = 4 and ab + b= 3

=> a = 2, a = -2 is rejected as a is positive.

=> 2b + b = 3

=> 3b = 3

=> b = 1

**The function is f(x) = 2x + 1**

## We’ll help your grades soar

Start your 48-hour free trial and unlock all the summaries, Q&A, and analyses you need to get better grades now.

- 30,000+ book summaries
- 20% study tools discount
- Ad-free content
- PDF downloads
- 300,000+ answers
- 5-star customer support

Already a member? Log in here.

Are you a teacher? Sign up now