Step-by-step explanation:
The sign or form of the numbers is irrelevant to the method. Arithmetic with any of integers, fractions, positive or negative numbers, decimals, percentages, roots or powers is all done in the usual way. While it is often nice to work with positive integers, your ability to do arithmetic should not be limited to numbers of that type.
As you already know, ...
- the product or quotient of two numbers with the same sign will be positive. (The product of an even number of minus signs is positive.)
- the product or quotient of two numbers with different signs will be negative. (The product of an odd number of minus signs is negative.)
- The sum of numbers with same signs will have that sign
- The sum of two numbers with different signs will have the sign of the number with the greatest magnitude. (3-2=1; -3+2=-1)
- Subtracting a number is the same as adding its opposite. (3-(-2) = 3+2)
- The sum of a number and its opposite is 0. (3 +(-3) = 3 -3 = 0)
These rules apply for all arithmetic, including the arithmetic you use in solving simultaneous equations.