How do you solve 3x+4y=-43x+4y=4 and x+2y=2x+2y=2 using substitution?

1 Answer
Jan 24, 2017

See the entire solution process below:

Explanation:

Step 1) Solve the second equation for xx:

x + 2y = 2x+2y=2

x + 2y - 2y = 2 - 2yx+2y2y=22y

x + 0 = 2 - 2yx+0=22y

x = 2 - 2yx=22y

Step 2) Substitute color(red)(2 - 2y)22y for xx in the first equation and solve for yy:

3(color(red)(2 - 2y)) + 4y = -43(22y)+4y=4

6 - 6y + 4y = -466y+4y=4

6 - 2y = -462y=4

6 - 6 - 2y = -4 - 6662y=46

0 - 2y = -1002y=10

-2y = -102y=10

(-2y)/color(red)(-2) = (-10)/color(red)(-2)2y2=102

(color(red)(cancel(color(black)(-2)))y)/cancel(color(red)(-2)) = 5

y = 5

Step 3) Substitute color(red)(5) for y in the solution to the second equation at the end of Step 1 and calculate x:

x = 2 - (2 xx color(red)(5))

x = 2 - 10

x = -8

The solution is:

x = -8 and y = 5 or (-8, 5)