The concept of (1): When the coefficients of the unknowns of two equations in an equation are equal or opposite, the unknowns are eliminated by adding or subtracting the two sides of the two equations, so that the binary linear equation is transformed into a univariate linear equation, and finally the solution of the equation is obtained. This method of solving equations is called addition, subtraction and elimination, or addition and subtraction for short.

(2) Add and subtract steps to solve binary linear equations.

① Using the basic properties of the equation, the coefficient of an unknown quantity in the original equation is transformed into an equal or opposite number;

(2) Using the basic properties of the equation, add or subtract two deformation equations to eliminate an unknown number, and get a linear equation (both sides of the equation must be multiplied by the same number, and it is forbidden to multiply only one side. If the unknown coefficient is equal, it will be subtracted, and if the unknown coefficient is opposite, it will be added);

③ Solve this one-dimensional linear equation and get the unknown value;

(4) Substituting the obtained value of the unknown quantity into any equation in the original equation to obtain the value of another unknown quantity;

⑤ Simultaneous two unknowns with "{"are the solutions of equations;

⑥ Finally, check whether the result is correct (substitute into the original equations and check whether the equations satisfy left = right).

For example:

{5x+3y=9①

{ 10x+5y= 12②

Enlarge ① by 2 times to get ③.

10x+6y= 18

③-② Obtain:

10x+6y-( 10x+5y)= 18- 12

y=6

Then bring y= into ①. ② or ③.

Solution: {x=- 1.8.

{y=6