Log in

View Full Version : Substition or Elimination


jimbot
Sep 16, 2009, 01:02 PM
I have this problem that I can't solve:

1/x + 1/y = 5/6
1/x - 1/y = 1/6


The book says the answer is (2,3)

Please help.

adam_89
Sep 16, 2009, 01:06 PM
So you are to show how to solve for x & y?

jimbot
Sep 16, 2009, 01:08 PM
So you are to show how to solve for x & y?

Yes

ArcSine
Sep 16, 2009, 02:42 PM
Add the two equations together, which leaves you with an equation in x only. After solving that for x, plug your x-value result back into both original equations and solve for y, making sure that your results for y are consistent.

morgaine300
Sep 16, 2009, 10:02 PM
In other words, use elimination. Note the y term is already a positive and negative of the same value, so you're all set to go. Don't let the fractions throw you off.

(Doing substitution would just be icky.)

KISS
Sep 16, 2009, 10:40 PM
So, just adding the equations gives you 2/x = 1

To make it look less icky, you can multiply top and bottom equations by 6 and add, but you can add 1/6 and 5/6 and you can subtract 1/y from 1/y and you can add 1/x and 1/x. The fractions should not intimidate you.