How do you solve y=2x+7; 3x-y=-9 using substitution method. Explain please!!

2 answers:

7 0

{ y = 2x + 7
{ 3x - y = - 9

Substitute y for 2x + 7 in the 2nd equation:

3x - y = - 9
3x - ( 2x + 7 ) = - 9
3x - 2x - 7 = - 9
3x - 2x = - 9 + 7
x = - 2

Substitute - 2 for x in one of the equations:

y = 2x + 7
y = 2.( - 2 ) + 7
y = - 4 + 7
y = 3

S = { - 2 , 3 }

eduard4 years ago

6 0

The y's value is given in the first equation. $y=2x+7$ . Now to solve, we will, plug it's value in the second equation.

$3x-(2x+7)=-9\\ \\ 3x-2x-7=-9\\ \\ x=-9+7\\ x=-2\\$

Now we have x's value, we will plug it's value in the first equation.(We can plug it in the second one too, but plugging it the first one will make it easier.)

$x=-2\\ y=2x+7\\ y=2\cdot -2+7\\ y=-4+7\\ y=3$

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