What is the value of the expression 2x2+3xy-y2, when x=2 and y=-4

Plug in 2 for x, and -4 for y

2(2)² + 3(2)(-4) - (-4)²

2² = 4(2) = 8
3(2) = 6(-4) = -24
-4² = 16

8 - 24 - 16 = answer

Simplify.

answer = 8 - 40
answer = -32

-32 is your answer

hope this helps