# SOLUTION: how do i solve the system using the substitution method for these two equations? {{{ -x-4y= -3 }}} {{{ 2x+y=15 }}}

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 Question 503170: how do i solve the system using the substitution method for these two equations? Answer by Maths68(1474)   (Show Source): You can put this solution on YOUR website!-x-4y= -3 ...........(1) 2x+y=15 .............(2) Take (1) -x-4y= -3 -x=4y-3 Multiply by (-1) both sides of above equation x=-4y+3 substitute the value of x in (2) 2(-4y+3)+y=15 -8y+6+y=15 -7y=15-6 -7y=9 Divide by -7 both sides of the above equation -7y/-7=9/-7 y=9/-7 Put the value of y in (1) -x-4(9/-7)= -3 Multiply by -7 both sides of the equation 7x-36=21 7x=21+36 7x=57 x=57/7 Solution set (57/7, -9/7) Check Put the values of x and y in either of two equations (1) or (2) -x-4y= -3 -57/7-4(-9/7)=-3 -57/7-4(-9/7)=-3 Multiply by 7 both sides -57-(4)(-9)=-3 * 7 -57+36=-21 -21=-21 2x+y=15 2(57/7)+(-9/7)=15 Multiply by 7 both sides 2(57)-9=15*7 114-9=105 105=105