Question

solve using reducable method : 30/x-y + 28/x+y=7. and. 21/x-y + 21/x+y=5

Answer 1

See,
Substitute 1/x-y as p
and 1/x+y as q

The equations would be then
30p +28q = 7
21p + 21q = 5

Solve for p and q. You can do it, right?

After getting values of p and q,

Resubstitute,
1/x-y = p
i.e. x-y = 1/p ....(1)

1/x+y =q
i.e. x+y =1/q....(2)


You can now solve equation 1 and 2 to get x and y