A (simple) System of Linear Equations

• Apr 15th 2009, 03:20 PM
tyler.
A (simple) System of Linear Equations
I've tried the 2 methods I know (Substitution and addition) and can't get an answer to this. Some of the answers I've gotten were 7(2/5) and 22 for x. It's just been so long since I've had to one of these!

(1/4)x - y = 7
x + 4y = 0
• Apr 15th 2009, 03:26 PM
icemanfan
Quote:

Originally Posted by tyler.
I've tried the 2 methods I know (Substitution and addition) and can't get an answer to this. Some of the answers I've gotten were 7(2/5) and 22 for x. It's just been so long since I've had to one of these!

(1/4)x - y = 7
x + 4y = 0

A solution using the method of addition:

(1/4)x - y = 7 is equivalent to x - 4y = 28 (multiply the equation by 4).

x - 4y = 28
x + 4y = 0
2x = 28

Thus, x = 14.

Then x + 4y = 0 becomes 14 + 4y = 0; 14 = -4y; y = -14/4 = -7/2.
• Apr 15th 2009, 03:31 PM
tyler.
Thanks for the help! I'm not sure where I went wrong with my addition... I think I may have forgotten to cancel out the 1/4 after multiplying by 4. (Although, wouldn't y = -3 1/2 at the end?)

Thanks!
• Apr 15th 2009, 11:07 PM
Twig
$\displaystyle -3.5 = -\frac{7}{2}$ (Cool)