Posted by **Jon** on Monday, February 18, 2008 at 11:39am.

Solve the matrix equation 2x + 5y = 1

x + 3y = 0 for y.

A)1

B)3

C)-3

D)-1

I chose D

2x + 5y = 1

y = 5 - 2x

x + 3(5 - 2x)= 0

x + 15 - 6x = 0

7x = 15

x = 15/7

I know thats wrong I don't know what to do

- Algebra(1 of 3) -
**drwls**, Monday, February 18, 2008 at 12:05pm
Your very first step is incorrect. Try this:

x + 3y = 0

x + 5/2 y = 1/2

Now subtract the last eq. from the first.

y/2 = -1/2

y = -1

- Algebra(1 of 3) -
**Reiny**, Monday, February 18, 2008 at 12:09pm
your solution is "riddled" with errors

2x + 5y = 1 solved for y is y = (1-2x)/5

not y = 5 - 2x like you had.

Even if it had been right, x + 15 - 6x = 0

becomes

-5x = -15 , not 7x=15 like you had

lets start over.

Why not solve the second equation for x? (look for the "single" variable)

x = -3y sub that back into the first

2(-3y) + 5y = 1

-y = 1

y = -1 looks like your D was the right guess.

- Algebra(1 of 3) -
**Anonymous**, Saturday, April 23, 2011 at 8:08am
- 15 x ² + 2x + 13 = 0

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