数学题（简便计算,
问题描述：
数学题（简便计算,
1 1-2+3-4+5……+101
2 498乘498-499乘497
3 26.04-（4.35除以1.5+0.9）乘4.2
4 3.01-0.25乘0.4除以0.25乘0.4
答
1:=(1-2)+(3-4)+(5-6).+(99-100)+101=-1 -1 -1...-1+101=512:498*498-499*497=498*498-(498+1)*(498-1)=498*498-498*498+498-498+1=13:=26.04-(2.9+0.9)*4.2=26.04-(4.0-0.2)*(4.0+0.2)=26.4-16+0.04=104:=3.01-0.25...