If $f(x) = 3x^2-x + 2$, find $f(a)$ and $[f(a)]^2$ If $f(x) = 3x^2-x^2$, find $f(a)$ and $[f(a)]^2$ 
Also, $2f(a) = 3x2(a)^2-2(a)+2 = 6a^2-2a+2$
The book says the answer is $6a^2-2a+4$. Why is that? Is the book wrong? 

what you are computing in your work sheet is $f(f(a).$ that is usually is different from $[f(a)]^2.$  you were asked to compute $[f(a)]^2 = (3a^2 - a + 2)^2 = 9a^4 + \dots +4.$
