First, find LCM of all the terms of an expressions & convert all of them into like terms by doing LCM on both the side of an equation. Now, you can cut the denominators on both side of an equation as they are same. Now, solve the equation as usual.

Sum

a/b + c/d = (ad + bc)/(bd)

Difference (is like the sum, only with c negative)

a/b - c/d = (ad - bc)/(bd)

In the above formulas, a, b, c, d can be any algebraic expression.

a/b + c/d = (ad + bc)/(bd)

Difference (is like the sum, only with c negative)

a/b - c/d = (ad - bc)/(bd)

In the above formulas, a, b, c, d can be any algebraic expression.