Question

Evaluate the expression 4y^2 -a if x = 2, y = -3, and a =6

Answer 1

The expression is telling you to proceed as follows:

• Pick some number $y$
• Pick some number $a$
• Compute the square of $y$
• Multiply it by 4
• Subtract $a$ from this result.

So, first of all, there's no point in fixing $x = 2$, because x doesn't appear in the expression. As for the evaluation, let's follow the aforementioned steps with fixed values:

Pick some number $y$

• Pick $y=-3$
• Pick $a=6$
• Compute $y^2 = (-3)^2 = 9$
• Multiply it by 4: $9 \cdot 4 = 36$
• Subtract $6$ from this result: $36-6=30$