数学题（简便计算,1 1-2+3-4+5……+1012 498乘498-499乘4973 26.04-（4.35除以1.5+0.9）乘4.24 3.01-0.25乘0.4除以0.25乘0.4

1：(1+3+5+7+……+101)-(2+4+6+8+……+100)=(1+101)×51÷2-(2+100)×50÷2=2601-2550=51
2:498*498-499*497=498*498-498*497-497=498*(498-497)-497=498-497=1
3:无简便计算
4：3.01-0.25*0.4/0.25*0.4=3.01-0.25/0.25*0.4*0.4=3.01-1*0.4*0.4=3.01-0.16=2.85

4. 2.01

1-2+3-4+5……+101
因为：1-2=-1，3-4=-1，5-6=-1 …… 99-100=-1 后面还有一个 101
所以：
1-2+3-4+5……+101
=50*（-1）+101
=51
498乘498-499乘497
498*498-499*497
=498*498 -（498+1）*（498-1）平方差公式
=498*498 - 498*498 -1 498*498可写为：498的平方
=-1
第三个不会
3.01-0.25乘0.4除以0.25乘0.4
3.01-0.25*0.4/0.25*0.4
=3.01-0.25/0.25*0.4*0.4
=3.01-0.16
=2.85

1.原式=(1-2)+(3-4)+(5-6)+……+(97-98)+(99-100)+101
=-1-1-1-1-……-1+101
=(-1)*100/2+101
=-50+101=51
2.原式=498^2-(498+1)(498-1)
=498^2-(498^2-1)
=498^2-498^2+1=1
3.原式=26.04-(2.9+0.9)*4.2
=26.04-3.8*4.2
=26.04-(4-0.2)(4+0.2)
=26.04-(4^2-0.04)
=26.04-16+0.04=10.08
4.原式=3.01-0.25/0.25*0.4*0.4
=3.01-0.16
=2.85

解:(1)原式=(1-2)+(3-4)+(5-6)**(99-100)+101
=(-1) X (100/2)+101
=-50+101
=51
(2)原式=498 X 498-499 X 497
=498^2-(498+1)(498-1)
= 498^2-(498^2-1)
=1
(3)原式=26.04-(2.9+0.9) X 4.2
=26.04-15.6
=10.44(没找到简单方法)
(4)原式=3.01-0.16
=2.85

1. 原式=（1-2）+（3-4）+…+101=（-1）*100/2+101=51
2.原式=498*498-（498+1）（498-1）=498*498-（498*498-1）=1
3.原式=26.04-（2.9+0.9）*4.2=26.04-15.96=10.08
4.顺序是什么？？？

1.原式＝(1+3+5+7+....+99)-(2+4+6+8+....100)+101=2500-2550+101=51括号里是等差数列
2.原式=498*498-(498+1)*497=498*498-498*497-497=498*(498-497)-497=1
3.原式＝26.04-[(1.35+2*1.5)除以1.5+0.9]*4.2=26.04-(0.9+2+0.9)*4.2=10.08
4.原式＝3.01-(0.25*0.4)除以(0.25*0.4)=3.01-0.1*0.1=3

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...

1 1-2+3-4+5……+101=1+（-2+3）+（-4+5）+……+（-100+101）=51；
2 498乘498-499乘497 = 498乘498-（498乘498-1）=1；
3 26.04-（4.35除以1.5+0.9）乘4.2 =[6.2-（4.35+1.35）除以1.5]乘4.2=（6.2-3.8）乘4.2=10.08；
4 3.01-0.25乘0.4除以0.25乘0.4 =3.01-0.4乘0.4=2.85。