Algebra(1 of 3)

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 that's wrong I don't know what to do

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  1. 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

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  2. 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.

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  3. - 15 x ² + 2x + 13 = 0

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