# How do you solve #x + y = 2# and #2x + y = -1# using substitution?

##### 1 Answer

Mar 7, 2016

#### Explanation:

Since

We then substitute this into the equation

So it becomes

Open the bracket and simplify.

#4 - 2y + y = -1#

#4 - y = -1#

Add

#4 - y + (1+y) = -1 + (1+y)#

#4 cancel(-y) + (1+cancel(y)) = cancel(-1) + (cancel(1)+y)#

#5 = y#

Substitute the value of

#x = 2 - y#

#= 2 - 5#

#= -3#

So we have

#x+y = -3 + 5 = 2#

#2x+y = 2(-3) + 5 = -1#

They match.