为什么变成了1-16分之7
追答解:原式 = (8/9) * (3/4 - 7/16 + 1/4) ←(拆小括号)
= (8/9) * (3/4 + 1/4 - 7/16) ←(加法交换律)
= (8/9) * (1 - 7/16) ←(3/4 + 1/4 = 1)
= (8/9) * (9/16)
= 1/2