Answer :
Multiply (x-y=10) by -2. You will get -2x+2y=-20.then multiply by 1 2x-y=17 that give u the same thing. Cross out the -2x and 2x then subtract 2y by y which will leave u with y and subtract -20 by 17 that will leave with -3 . So y= -3
another way to do it is
2x-y=17
x-y=10, x=10+y
substitute x=10+y for x in 2x-y=17 and get
2(10+y)-y=17
20+2y-y=17
20+y=17
subtract 20 from both sides
y=-3
subsitute y=-3 into equation x-y=10
x-(-3)=10
x+3=10
subtract 3 from both sides
x=7
or subsitute into 2x-y=17
2x-(-3)=17
2x+3=17
subtract 3 from both sides
2x=14
divide both sides by two
x=7
2x-y=17
x-y=10, x=10+y
substitute x=10+y for x in 2x-y=17 and get
2(10+y)-y=17
20+2y-y=17
20+y=17
subtract 20 from both sides
y=-3
subsitute y=-3 into equation x-y=10
x-(-3)=10
x+3=10
subtract 3 from both sides
x=7
or subsitute into 2x-y=17
2x-(-3)=17
2x+3=17
subtract 3 from both sides
2x=14
divide both sides by two
x=7
