Question

Solve the system by substitution.
{2x-y+z=-4
{z=5
{-2x+3y-z=-10

Answer 1

So, you have that z=5. Now change everywhere, where is z, to 5. what do you get?

Answer 2

2x-y+5=-4
-2x+3y-5=-10

Answer 3

so, now you should substitute one variable with another. It should be done leaving one variable (without any numbers or any minuses near it):

2x-y+5=-4
-y=-4-5-2x
-y=-9-2x|:(-1) (I do this to eliminate the minus near variable "y". Don't forget, when you divide a number by a negative number, it changes it sign)
y=9+2x

No, insert 9+2x into the third equation and solve it. What do you get?

Answer 4

-2x+3(9+2x)-5=-10 like this?

Answer 5

yes, you are absolutely right. NDo you know how to solve this equation?

Answer 6

not really

Answer 7

okay, I will help you.
-2x+3(9+2x)-5=-10
-2x+27+6x-5=-10
-2x+6x+22=-10
4x=-32|:4
x=-8

Do you understand how I did it?

Answer 8

I think so!! what would be the equation for the first problem?

Answer 9

um,sorry, I didn't uderstand? So, now you have that x=-8 and z=5, right? Now you have to find the y... Don't forget, that you have equation
y=9+2x
so y is:
y=9+2*(-8)=9-16=-7

Your answer is (-8;-7;5)

Answer 10

okay i get it thank you so much!

Answer 11

you are welcome;))