Evaluate xy for x = –9 and y = 5.
A –4
B 45
C –45
D –14

C. -45

These types of problems can be fairly simply once you understand substitution. Substitution is when we put in values (in this case -9 and 5) in their set variable (x and y in this case.)

The problem states that x=-9 therefore we put in -9 for x in the multiplication of xy so it looks like this: (-9)(y). Next we want to substitute in the y value which is 5 so that we now have (-9)(5).

Because there is no plus or minus sign, along with a division sign, we then MULTIPLY these two numbers because the variables are connected so -9*5 would equal to -45.

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