Math check 3
posted by Shawn .
f(x) = 1/(x+7)+15/(x8). Find all a for which f(a)=f(a+15).
I understand this so far
f(a)=f(a+15)
1/(7+a) + 15/(a8) = 1/(a+22) + 15/(a+7)
I have multiplied the LCD of (a8)(a+7)(a+22)by both sides with no luck.
This is a multiple choice question
a.) 161/8
b.) 120/7
c.) 161/7
d.) 17
I have the answer as
Responses
Math problem still stuck  Ryan, Sunday, October 12, 2008 at 4:05pm
Just plug in the values since it's multiple choice.
Math problem still stuck  Shawn, Sunday, October 12, 2008 at 4:12pm
When I plug in the values what am I looking to find?
Math problem still stuck  bobpursley, Sunday, October 12, 2008 at 4:20pm
If you want to plug in, plug in the answer for a to see if both sides are equal.
Math problem still stuck  Ryan, Sunday, October 12, 2008 at 4:21pm
you want 1/(7+a) + 15/(a8) = 1/(a+22) + 15/(a+7), your second equation, to be true, so you true the four values of a given in the equation and if both sides are equal, you've found it.
Math problem still stuck  Ryan, Sunday, October 12, 2008 at 4:22pm
*try not true
Math problem still stuck  Shawn, Sunday, October 12, 2008 at 4:32pm
So you are saying that it is none of the multiple choice answers of 161/8,
120/7, 161/7, or 17
?

I don't think Ryan said the answers is none. He said try them to see if both sides are equal. I think it was me a couple of threads ago that I told you to go through it once more to see if it works, that I did it in my head and didn't get any of the answers.
I don't know what is the problem here. If you want to plug the given answers in for a, do it. If not, don't. 
I get 21 1/16
In other words none of the above. 
(a+15)(a+7)