When is the addition and subtraction elimination method to use formula 1 minus formula 2? Yes or add formula 2? Or use formula 2 minus Formula 1?

When is the addition and subtraction elimination method to use formula 1 minus formula 2? Yes or add formula 2? Or use formula 2 minus Formula 1?

Match the coefficients of an unknown number into the same, larger, smaller, or positive, depending on the actual situation

The method of adding, subtracting and eliminating elements for binary linear equation (when to add, when to subtract, how to add and how to subtract)

Basic properties of inequality?

Basic property 1: add or subtract the same integral on both sides of the inequality, and the direction of the inequality sign does not change,
Basic properties: both sides of the inequality multiply (or divide) the same integer greater than 0 at the same time, and the direction of the inequality sign does not change
Basic properties: both sides of the inequality multiply (or divide) the same integer less than 0 at the same time, and the direction of inequality sign changes