Question

Find whether (m,m) lies on linear y-x=0, or not?

Answer 1

Simply plug the point into the given line equation and see if it gives a true statement : 
$y-x=0\\m-m=0\\0=0$
which is true. so the point $(m,m)$ lies on line $y-x=0$

Answer 2

To find the particular point lie on the equation ,for this we should put the value of point on equation.If it satisfy the equation. Then point will definitely lie on equation
point is (m,m)
equation is y-x=0
m-m=o which is true
Hence point (m,m) will lie on equation