SOLUTION: If f(x)=x^2+2x+8, then what does f(x+9) equal?

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: If f(x)=x^2+2x+8, then what does f(x+9) equal?      Log On


   

Question 557537: If f(x)=x^2+2x+8, then what does f(x+9) equal?
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
f%28x%29=x%5E2%2B2x%2B8 Start with the given function


f%28x%2B9%29=%28x%2B9%29%5E2%2B2%28x%2B9%29%2B8 Replace EVERY 'x' with 'x+9'


f%28x%2B9%29=x%5E2%2B18x%2B81%2B2%28x%2B9%29%2B8 FOIL


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Side note:

So %28x%2B9%29%5E2+=+x%5E2%2B18x%2B81


We are using the FOIL rule: First, Outer, Inner, Last and this means that we multiply the "first" terms, then the "outer" terms, then the "inner" terms, then finally the "last" terms. We then add up these products.

For a more in-depth look at expanding this, check out this link
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f%28x%2B9%29=x%5E2%2B18x%2B81%2B2x%2B18%2B8 Distribute


f%28x%2B9%29=x%5E2%2B20x%2B107 Combine like terms.


So the answer is f%28x%2B9%29=x%5E2%2B20x%2B107