In the fourth grade of primary school, the textbooks of previous years began to learn the initial understanding of equations in the fourth grade. Mainly through the balance principle to know and understand. Solve the equation by using the properties of the equation, that is, both sides of the equation increase or decrease the same number at the same time, and the equation holds. When both sides of the equation are multiplied or divided at the same time (except 0), the equation is still valid. Now there is no equation in the fourth grade of primary school.