过O点分别画出AB、AC的垂线．
能简算的要简算．
3.2×1.25×0.255.8×[1÷（2.1﹣2.09）]
×101﹣．
脱式计算（能简算的要简算）
17.64÷4.9+6.733.4÷[（1.2+0.5）×5]1.9+19.9+199.9+0.30.25×12.5×3.2．
脱式计算（怎样算简便就怎样算）．
（18.6﹣18.6÷3.1）×1.6
12.5×2.5×3.2
4.5÷18
32.9×0.46+5.4×3.29．
脱式计算．
4.27﹣1.72+0.73﹣2.281.25×8.37×0.8
7.8﹣7.8÷（1.3×1.5）5.28+5.28×9．
脱式计算 （能简算的要简算）．
72.8÷5.6+1.4958.1﹣29.7÷330.94﹣5.09﹣4.91
3.94+34.3×0.25.4×2.3+5.4×7.73.2×12.5×0.25．