# SOLUTION: My daughter is supposed to solve this problem using substitution. I don't get it. The problem is: -7x-2y= -13 x-2y=11 Can you help me try to explain this to her?

Algebra ->  Algebra  -> Expressions-with-variables -> SOLUTION: My daughter is supposed to solve this problem using substitution. I don't get it. The problem is: -7x-2y= -13 x-2y=11 Can you help me try to explain this to her?      Log On

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 Question 256543: My daughter is supposed to solve this problem using substitution. I don't get it. The problem is: -7x-2y= -13 x-2y=11 Can you help me try to explain this to her?Found 2 solutions by Alan3354, ankor@dixie-net.com:Answer by Alan3354(30993)   (Show Source): You can put this solution on YOUR website!-7x-2y= -13 x-2y=11 --> x = 2y+11 ------------- Sub for x into the 1st eqn -7(2y+11) - 2y = -13 -14y-77 - 2y = -13 -16y = 64 y = -4 --------- sub for y into either eqn x-2y=11 x-2(-4) = 11 x+8 = 11 x = 3 Answer by ankor@dixie-net.com(15649)   (Show Source): You can put this solution on YOUR website!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 = 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 = x = +3 : : Check solutions in the 2nd equaiton x-2y=11 3 - 2(-4) = 11 3 + 8 = 11; confirms our solutions