Question

Solve the system of equations 2x+3y=1 y=3x+15 (___,___)

Answer 1

{2x+3y=1
{y=3x+15

2x+3(3x+15)=1

2x+9x+45=1

11x=-44

x=-4

y=3*(-4)+15

y=-12+15=3

y=3

The answer  (-4; 3)

Answer 2

2x + 3y = 1
y = 3x + 15

Get the same variables on each side

3y = 1 - 2x
y = 15 + 3x

Multiply both sides of that second equation by 3 so we can subtract.

3y = 1 - 2x
3y = 45 + 9x

Subtract the equations from each other.

0 = -44 - 11x

Solve.

44 = -11x
-4 = x

Use x in an earlier equation to find y.

y = 3x + 15
y = 3 * -4 +15
y = -12 + 15
y = 3

x = -4, y = 3