GRE 8767 #20

Forum for the GRE subject test in mathematics.
d555
Posts: 1
Joined: Fri Oct 03, 2014 10:24 pm

GRE 8767 #20

Postby d555 » Sat Oct 18, 2014 2:56 pm

Suppose that f(x+1)=f(x) for all real x. If f is a polynomial and f(5) = 11, the f(15/2) is:

a)-11
b) 0
c)11
d) 33/2
e)not uniquely determined by the information given

I thought answer e) but actually it's c), I don't figure out why?

mathblob23481
Posts: 4
Joined: Sun Oct 19, 2014 12:09 am

Re: GRE 8767 #20

Postby mathblob23481 » Sun Oct 19, 2014 12:11 am

The key is to realize that f is a polynomial and use the fact that f(5) = 11 with f(x) = f(x+1) for all real x to deduce it must be constant. Hence, you can obtain f(7.5).




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