If it is an equation, such as x=2, you can add (or subtract) the same number left and right, such as x+ 1=2+ 1.

X=2 again.

In the equation, it is often said that adding left and subtracting right, that is, adding and subtracting both sides at the same time, just offsets the monomial of its opposite number.

The essence of the fractional equation upstairs is to multiply or divide the same number from left to right at the same time. If simplified, it is the cross multiplication upstairs. If it's not enough, you can tell me again and I'll add it.