Question

Someone explain this:

http://tutorial.math.lamar.edu/Extras/AlgebraTrigReview/SolveSystems.aspx


the first problem..

Answer 1

where does the -2 come from???

Answer 2

he multiplied by -2 so the z's could be negative to each other, so when he added them together, they would cancel out

Answer 3

Why not -1?

Answer 4

Silly, nevermind!

Answer 5

because then it would be 4z -2z
and that wouldnt cancel out

Answer 6

Thanks haha I realized that ...Im on an empty stomach lol