初中代数第一册第120页列举了四个式子: 1+2=3,a+b=b+a,S=ab,4+x=7作为等式的例子,接着给出方程定义:“含有未知数的等式叫做方程”,并且指出“4+x=7是一个方程”。等式1+2=3不含有未知数,因而不是方程,这是显然的; Four books are listed on page 120 of the first edition of junior high school algebra: 1+2=3, a+b=b+a, S=ab, and 4+x=7 as examples of equations, followed by equations: “The equation with unknowns is called an equation,” and states that “4+x=7 is an equation.” Equation 1+2=3 does not contain an unknown number and is therefore not an equation, which is obvious;