substitution for 4x+y=9 and y=-7
{y=-7
{4x+y=9 Substitute y.
4x+(-7)=9
4x-7=9 /+7
4x=16 /:4
x=4
Solution; (4; -7)
4x + y = 9y = -7Plug it in:4x - 7 = 9Add 7 to both sides:4x = 16Divide 4 to both sides:x = 4Plug this back into the equation:4x + y = 94(4) + y = 916 + y = 9Subtract 16 to both sides:y = -7So our solution is (4, -7)
