Solve the following system of equations?

Question

I'm stuck on this. I have to find what x and y is from these two system of equations:

-3x - 4y = 14
7x + 6y = -6

I already know that you multiply both equations to cancel either x or y out of them to solve the other first. But I keep getting it wrong...

Answer 1

Elimination method

Given equation -3x - 4y = 14

Multiple to each side by 7

-21x - 28y = 98 --------> (1)

And equation 7x + 6y = -6

 

Multiple to each side by 3

21x + 18y = -18  -------> (2)

To eliminate the x value add the equations (1) and (2).

-21x - 28y = 98

21x + 18y = -18

__________

-10y = 80

Divide to each side by 10.

-10y / -10 = 80 / -10

⇒ y = -8

Substiute the y value in (1).

-3x - 4*-8 = 14

-3x + 32 = 14

-3x = 14 - 32

-3x = -18

x = -18/-3

⇒ x = 6

Solution x = 6, y = -8.