SOLUTION: I could use some help in understanding this problem from a homework sheet. If f(x)=x^2+2x,find f(-1). thank you.

Algebra ->  Functions -> SOLUTION: I could use some help in understanding this problem from a homework sheet. If f(x)=x^2+2x,find f(-1). thank you.       Log On


   

Question 137853: I could use some help in understanding this problem from a homework sheet. If f(x)=x^2+2x,find f(-1). thank you.
Answer by vleith(2983) About Me  (Show Source):
You can put this solution on YOUR website!
You are given a function f%28x%29=x%5E2%2B2x
You then asked to evaluate that function at f(-1).
All you need to do it substitute -1 for x everywhere in the function and then simply the result.
f%28x%29=x%5E2%2B2x
f%28-1%29=%28-1%29%5E2%2B2%2A%28-1%29
f%28-1%29=1+%2B+%28-2%29
f%28-1%29+=+1+-+2
f%28-1%29+=+-1+
So given an input of -1, the function evaluates to -1.
Now let's find f(2)
f%28x%29=x%5E2%2B2x
f%282%29=%282%29%5E2%2B2%2A%282%29
f%282%29=4+%2B+4%29
f%282%29+=+8
And so on.
Get it?