748.
(x-2y)²+4(x-2y)+4
(x-2y)²+2×(x-2y)×2+2²
(x-2y+2)²
750.
16m²-8m(3-m)+(3-m)²
(4m-(3-m))²
(4m-3+m)²
(5m-3)²
