Answer:
Here is a way one of my math teachers taught me.
For + x + = +:
In elementary school, you were taught by your math teacher that an positive number multiplied with a positive number is equal to a positive number. To solve, use basic rules of multiplications.
For + x - = -:
Think of it this way. There are two line segments that makes a positive sign. When multiplying, you are subtracting a line, which would result in a negative sign. Whenever a positive multiplies a negative, it is always a negative outcome.
For - x - = +:
There are two lines given (two negatives). When multiplied, the two lines make a positive sign (which is made by drawing two lines). This shows that two negative numbers multiplied or divided together will make a positive sign .
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