Question

If 7x-9y=25 and 9x-7y=23 then find x-y

Answer 1

7x-9y=25 (eq.1)
9x-7y=23 (eq.2)

Add eq. 1 and 2

7x-9y=25
9x-7y=23
+
16x-16y=48
= x-y=3 (eq.3)

Subtract eq.1 and 2

7x-9y=25
9x-7y=23
- +. -
-2x -2y =2
= -x-y=2 (eq.4)

from eq. 3 and 4

x-y=3
-x-y=2
-2y=5
y=-5/2

put value of y in eq. 4
-x-(-5/2)=2
-x+5/2=2
-x=2-5/2
-x= 4-5/2
-x=-1/2
x=1/2