document.write( "Question 257618: Suppose that f(x) = ax + b, where a and b are real numbers.
\n" ); document.write( "Given that f(f(f(x))) = 8x + 21, what is the value of a + b? \n" ); document.write( "

Algebra.Com's Answer #189509 by jim_thompson5910(35256) $\"\"$ $\"About$

You can put this solution on YOUR website!
Hint: Starting with $\"f%28x%29=ax%2Bb\"$ , plug in $\"ax%2Bb\"$ for 'x' to get $\"f%28f%28x%29%29=a%28ax%2Bb%29%2Bb\"$ . Do so again to get $\"f%28f%28f%28x%29%29%29=a%28a%28ax%2Bb%29%2Bb%29%2Bb\"$ . Now simplify to get $\"f%28f%28f%28x%29%29%29=a%5E3x%2Ba%5E2b%2Bab%2Bb\"$ . From here, just equate the two expressions and solve for 'a' and 'b'. \n" ); document.write( "

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