First of all, if an equation has two variables, it cannot be solved directly, so we must get an equation with only one variable from the equations of multiple equations through various transformations, and then we can solve this variable directly.

2 Yuan's 1 degree equation, each equation has two variables, so we must find a way to get rid of one, so that we can solve it directly. If you remove a variable, this is elimination.

Secondly, substitution elimination is a kind of elimination, and the way is substitution. Replace what? Substituting one of the variables, what do you think of the following:

An equation, such as (1), 5x+ 80 = 6y+20, can be solved no matter what Y is, and 5x = 6y-60 =>；; x = 1.2y - 12

This is an expression of x, with the variable y in it. It doesn't matter, this expression is obtained from equation 1, because it is the expression of X, so we have to substitute X into equation 2:

4y = 2x+80 = 2 *( 1.2y- 12)+80 = & gt； 4y = 2.4y -24 + 80 = > 1.6y = 56

= & gty = 35

Note: Why can't the equation 1 be brought in? Because the expression derived from equation 1 replaces equation 1, only the result of 0=0 can be obtained, which cannot be used to solve y, but it can be used to verify whether the expression is wrong.

Find y again, and then calculate x according to the expression: x =1.2y-12.

x = 1.2y- 12 = 1.2 * 35- 12 = 30

Finally, you can not do it. Substitute X = 30 and Y = 35 into the original equation to check.

Summary: In short, the steps are as follows

1) Derive the expression of X = containing y or Y = containing x from 1 equations.

2) Substitute the variables on the left side of the expression into another equation to get a unary equation. Solve this variable

3) Substitute the solution result into the expression to get the solution of another variable.

4) check