SOLUTION: what is 2x+4y=30 -2x-2y=-21.5 i dont understand how to do this

Algebra ->  Coordinate Systems and Linear Equations  -> Lessons -> SOLUTION: what is 2x+4y=30 -2x-2y=-21.5 i dont understand how to do this      Log On


   

Question 1010075: what is 2x+4y=30 -2x-2y=-21.5 i dont understand how to do this
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

2x%2B4y=30+
-2x-2y=-21.5+
here you are given two linear equations ( both graph is a line)
you need to solve this system and find x and y value that makes both equations true


2x%2B4y=30+
-2x-2y=-21.5+
--------------------add both to eliminate one unknown variable, in your case you can eliminate 2x and -2x
2x%2B4y%2B%28-2x-2y%29=30+%2B%28-21.5%29
cross%282x%29%2B4y-cross%282x%29-2y=30+-21.5
4y-2y=8.5
2y=8.5
y=8.5%2F2
y=4.25
now, go back to 2x%2B4y=30+, substitute 4.25 for y and solve for x
2x%2B4%2A4.25=30+
2x%2B17=30+
2x=30+-17
2x=13
x=13%2F2
x=6.5
so, your lines are intersecting in one point and that point is:
(6.5,4.25)

let's see it on a graph: