(二分之一x-2y)^2
=(x/2)²-2×x/2×2y+(2y)²
=x²/4-2xy+4y²
(2xy+五分之一x)^2
=(2xy)²+2×2xy×x/5-x²
=4x²y²+4x²y/5-x²
(n+1)^2-n^2
= n²+2n+1-n²
=2n+1
(二分之一x-2y)^2
=(x/2)²-2×x/2×2y+(2y)²
=x²/4-2xy+4y²
(2xy+五分之一x)^2
=(2xy)²+2×2xy×x/5-x²
=4x²y²+4x²y/5-x²
(n+1)^2-n^2
= n²+2n+1-n²
=2n+1