[(x+2y)(x-2y)-(x+4y)²]÷4,其中x=5,y=-2

[(x+2y)(x-2y)-(x+4y)²]÷4,其中x=5,y=-2
[(x+2y)(x-2y)-(x+4y)²]÷4,其中x=5,y=-2

[(x+2y)(x-2y)-(x+4y)²]÷4,其中x=5,y=-2
解
[(x+2y)(x-2y)-(x+4y)²]÷4
=(x²-4y²-x²-8xy-16y²)÷4
=(-8xy-20y²)÷4
=-2xy-5y²
=-2×5×(-2)-5×4
=20-20
=0

=[(5-4)*(5+4)-(5-8)^2]/4
=(9-9)/4
=0