Solve the following system of equations by elimination:
5x+4y=12
3x-3y=18
We'll take advantage of the y's having opposite signs and select it for elimination:
Multiply the first equation by 3 and the second by 4:
3*(5x+4y)=3*12
15x+12y=36
Now for the second:
4*(3x-3y)=4*18
12x-12y=72
Adding the two new equations:
15x+12y+12x-12y=36+72
Simplifying:
27x=108
Solving:
x=108/27=4
x=4
Now to find the value of y, we can use any of the equations:
5x+4y=12
Substitute x=4
5*4+4y=12
20+4y=12
4y=12-20=-8
Solving:
y=-8/4=-2
y=-2
Solution: x=4, y=-2