.1x+.2y=-1
.5x-.9y=6.4
×-5 equation .1x+.2y=-1
-.5x-y=5
.5x-.9y=6.4
solve by elimination
-1.9y=11.4
÷-1.9 both sides
y=-6
solve for X
.1x+.2 (-6)=-1
.1x-1.2=-1
+1.2 both sides
.1x=.2
÷ 1 both sides
x=2
plug into 2nd equation to see if it's true
x=2
y=-6
0.5(2)-0.9(-6)=6.4
1+5.4=6.4
6.4=6.4 answers hold true