How do you solve -2x+3y=152x+3y=15 and -6x+6y=186x+6y=18 using substitution?

1 Answer
Mar 28, 2018

See a solution process below:

Explanation:

Step 1) Solve the second equation for yy:

-6x + 6y = 186x+6y=18

(-6x + 6y)/color(red)(6) = 18/color(red)(6)6x+6y6=186

(-6x)/color(red)(6) + (6y)/color(red)(6) = 36x6+6y6=3

-x + y = 3x+y=3

-x + color(red)(x) + y = 3 + color(red)(x)x+x+y=3+x

0 + y = 3 + x0+y=3+x

y = 3 + xy=3+x

Step 2) Substitute (3 + x)(3+x) for yy in the first equation and solve for xx:

-2x + 3y = 152x+3y=15 becomes:

-2x + 3(3 + x) = 152x+3(3+x)=15

-2x + (3 xx 3) + (3 xx x) = 152x+(3×3)+(3×x)=15

-2x + 9 + 3x = 152x+9+3x=15

-2x + 9 - color(red)(9) + 3x = 15 - color(red)(9)2x+99+3x=159

-2x + 0 + 3x = 62x+0+3x=6

-2x + 3x = 62x+3x=6

(-2 + 3)x = 6(2+3)x=6

1x = 61x=6

x = 6x=6

Step 3) Substitute 66 for xx in the solution to the second equation at the end of Step 1 and calculate yy:

y = 3 + xy=3+x becomes:

y = 3 + 6y=3+6

y = 9y=9

The Solution Is:

x = 6x=6 and y = 9y=9

Or

(6, 9)(6,9)