Question 256543
substitution. I don't get it. The problem is:
-7x - 2y = -13
x - 2y = 11
:
Choose one of the equation to use for substitution, the 2nd equation
x - 2y = 11
Add 2y to both sides
x = 2y + 11
:
Now we can substitute (2y+11) for x in the 1st equation, find y
-7x - 2y = -13
-7(2y+11) - 2y = -13
Multiply what's inside the brackets by -7
-14y - 77 - 2y = -13
add 77 to both sides
-14y - 2y = - 13 + 77
do the math
-16y = +64
The variable has to be positive, multiply both sides by -1
16y = -64
Divide both sides by 16
y = {{{(-64)/16}}}
y = -4
:
Solve for x in the 1st equation, substitute -4 for y in the 1st equation
:
-7x - 2y = -13
-7x - 2(-4) = -13
-7x + 8 = -13 Subtract from both sides
-7x = -13 - 8
-7x = -21
Multiply both sides by -1
7x = 21
x = {{{21/7}}}
x = +3
:
:
Check solutions in the 2nd equaiton x-2y=11
3 - 2(-4) = 11 
3 + 8 = 11; confirms our solutions