①21×36+36×21=36×21+21×4+21×32=21×（4+36）+21×32=21×40+21×32=21×40+21×30+21×2=21×（40+30）+42=21×70+42=1470+42=1512②72×26 +36×48=2×36×26+36×48=36×52+36×48=36×（52+48）=36×1...