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23x0.1+2.3x9.9怎么样简便计算

23*0.1+2.3*9.9 =2.3+2.3*(10-0.1) =2.3+23-0.23 =25.3-0.23 =25.07

2.1×9.9+0.21简便计算如下: 2.1×9.9+0.21 =2.1x9.9+0.21x1 =2.1x9.9+2.1x0.1 =2.1x(9.9+0.1) =2.1x10 =21

0.1+0.2+0.3.........+9.8+9.9 =(0.1+9.9)X99÷2 =10x99÷2 =495

(1)∵方程两边开方得,x-1=±3,∴x1=4,x2=-2;(2)∵原方程可化为(x-2)(2-3x)=0,∴x-2=0或2-3x=0,解得x1=2,x2=23;(3)∵a=b=c=1,∴△=b2-4ac=1-4=-3<0,∴此方程无解;(4)原方程可化为(x2-3x+94-94)-2=0,即(x-32)2=174两边开方得...

8.1×1.9+0.9×1.9+1.9 =(8.1+0.9+1)x1.9 =10x1.9 =19 0.1+1.9×3.2 =0.1+2x3.2-0.1x3.2 =0.1+6.4-0.32 =6.5-0.32 =6.18

1.72+0.53+0.28+1.47 =(1.72+0.28)+(0.53+1.47) =2+2 =4 3.2×1.25×2.5 =4×0.8×1.25×2.5 =(4×2.5)×(0.8×1.25) =10×1 =10 3.9×99 =3.9×(100-1) =3.9×100-3.9×1 =390-3.9 =386.1

根据题意, 就是0.21+0.79=1, 就是这个意思。

1)3x²-12=0 3x²=12 x²=4 x=2或-2 2)(y+2)²=9 y+2=3或y+2=-3 y=1或y=-5 3)x²-2x-4=0 x²-2x=4 x²-2x+1=5 (x-1)²=5 x-1=√5或x-1=-√5 x=√5+1或x=-√5=1 4)x(x-7)=5x-36 x²-7x=5x-36 x²-12x+36=...

∵函数f(x)=3x+3x-9,∴f(1)=-3,f(2)=6,∴f(1)f(2)<0.再根据函数零点的判定定理可得函数f(x)=3x+3x-9的零点一定位于区间(1,2),故选:C.

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