Homework Help: Algebra(1 of 3)

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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