# Function analysis

• Nov 22nd 2011, 04:52 PM
benny92000
Function analysis
If g(x-1)= x^(2) + 2, then g(x)=?

Answer = x^(2) + 2x + 3

Thanks for the help
• Nov 22nd 2011, 05:10 PM
emakarov
Re: Function analysis
Let's define f(x) = g(x - 1) = x^2 + 2. Then what is f(x + 1)?
• Nov 22nd 2011, 05:15 PM
Prove It
Re: Function analysis
Quote:

Originally Posted by benny92000
If g(x-1)= x^(2) + 2, then g(x)=?

Answer = x^(2) + 2x + 3

Thanks for the help

\$\displaystyle \displaystyle g(x) = g(x - 1 + 1)\$, so if \$\displaystyle \displaystyle g(x - 1) = x^2 + 2\$ then \$\displaystyle \displaystyle g(x) = (x + 1)^2 + 2 = x^2 + 2x + 1 + 2 = x^2 + 2x + 3\$.
• Nov 22nd 2011, 05:31 PM
emakarov
Re: Function analysis
Quote:

Originally Posted by Prove It
\$\displaystyle \displaystyle g(x) = g(x - 1 + 1)\$, so if \$\displaystyle \displaystyle g(x - 1) = x^2 + 2\$ then \$\displaystyle \displaystyle g(x) = (x + 1)^2 + 2 = x^2 + 2x + 1 + 2 = x^2 + 2x + 3\$.

Strictly speaking, one needs to consider g((x+1)-1): this is the result of substituting x+1 for x in the expression for g(x-1).
• Nov 24th 2011, 11:50 AM
HallsofIvy
Re: Function analysis
Yet another approach: given g(x- 1)= x^2+ 2, let y= x- 1 so that x= y+ 1. Then g(x- 1)= g(y)= (y+ 1)^2+ 2= y^2+ 2y+ 3. And, of course, it follows that g(x)= x^2+ 2x+ 3.