How do you solve the following system?: $3 x + 3 y = - 21, 4 x - 3 y = 15$ $3x+3y=-21 , 4x-3y=15$

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Answer 1 · 2016-06-04T22:08:23

$x = - \frac{6}{7}, y = - \frac{129}{12}$ $x=-6/7, y=-129/12$

use the addition/elimination method to solve for x.

$3 x + 3 y = - 21$ $3x+3y=-21$
$4 x - 3 y = 15$ $4x-3y=15$

3x + 4x = 7x, 3y - 3y = 0 and -21 + 15 = -6

$:.7x=-6$ so $x=-6/7$

sub in and test

$3(-6/7)+3y=-21$
$-18/7+3y=-21$

multiply everything by 7 to eliminate the fraction

$-18+21y=-147$

$21y=-129$

$y=-129/12$

.

$4(-6/7)-3y=15$
$-24/7-3y=15$

multiply everything by 7 to eliminate the fraction

$-24-21y=105$

$-21y=129$

$y=-129/12$

How do you solve the following system?: 3x+3y=-21 , 4x-3y=15 3x+3y=−21,4x−3y=153x+3y=-21 , 4x-3y=15