知识大全 a=12+3,求1?2a+a2a?1?a2?2a+1a2?a的值
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a=12+3,求1?2a+a2a?1?a2?2a+1a2?a的值
∵a=
1 | ||
2+
|
=2-
3 |
,
∴a-1<0,
∴原式=
(a?1)2 |
a?1 |
+
a?1 |
a(a?1) |
=a-1+
1 |
a |
=2-
3 |
-1+2+
3 |
=3.
(x+y)^2(x-y)^2(x^4+x^2y^2+y^4)^2
(x+y)^2(x-y)^2(x^4+x^2y^2+y^4)
= (x+y) (x-y) ^2 (x^4+x^2y^2+y^4)
= ( x^2-y^2 )^2 (x^4+x^2y^2+y^4)
= ( x^2-y^2 ) ( x^2-y^2 ) (x^4+x^2y^2+y^4)
= ( x^2-y^2 ) ( x^2)^3 - (y^2) ^3
= ( x^2-y^2 ) ( x^6-y^6 )
= x^(2+6) - x^6y^2 - x^2y^6 + y^(2+6)
= x^8 - x^6y^2 - x^2y^6 + y^8
[(a-2b)^2-4(a-2b)+4]除以(a-2b-2)
[(a-2b)^2-4(a-2b)+4]÷(a-2b-2)
=(a-2b-2)^2÷(a-2b-2)
=a-2b-2
求(lg50)^2+lg2*lg(50)^2+(lg2)^2
lg50)^2+lg2*lg(50)^2+(lg2)^2
=(lg50)^2+lg2*lg[(50)^2]+(lg2)^2
=(lg50)^2+2lg2*lg(50)+(lg2)^2
=(lg50+lg2)^2
=[lg(50*2)]^2
=(lg100)^2
=(lg10^2)^2
=(2lg10)^2
=(2*1)^2
=2^2
=4.
na2o2+h2o —h2o2+?
Na2O2+2H2O=H2O2+2NaOH
已知2a-b=5,那么2(2a-b) 2 -3(b-2a)+8=______
把2(2a-b) 2 -3(b-2a)+8整理得: 2(2a-b) 2 -3(-2a+b)+8=2(2a-b) 2 +3(2a-b)+8, 又∵2a-b=5, ∴2(2a-b) 2 +3(2a-b)+8, =2×5 2 +3×5+8, =50+15+8, =65+8, =73. |
2/3+2/15+2/35+2/63+2/99=
2/3+2/15+2/35+2/63+2/99
=2/(1x3)+2/(3x5)+2/(5x7)+2/(7x9)+2/(9/11)
=1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11
=1-1/11
=10/11
(1)计算: (- 1 2 ) -3 + ( 2 -5) 2 +2sin45° (2)解方
(1)原式=-8+5-
=-3; (2)原方程两边同乘以(x-3)可化为:2-x+3(x-3)=-2
.
是方程的根. |
计算:(1)?32×[?32×(?23)2+(?2)3](2)-22-32÷[(-2)3-(-1)2
(1)原式=-
3 |
2 |
×[-9×
4 |
9 |
-8]
=-
3 |
2 |
×[-4-8]
=-
3 |
2 |
×(-12)
=18.
(2)原式=-4-9÷[-8-1]
=-4-9÷(-9)
=-4+1
=-3.
数列求和1^2+2^2+3^2+…+(n-1)^2
(n+1)^3-n^3=3n^2+3n+1
1^2=1
2^3-1^3=3*1^2+3*1+1
3^3-2^3=3*2^2+3*2+1
.................................
(n+1)^3-n^3=3*n^2+3n+1
累加得:
(n+1)^3=2Sn+3(1+2+....+n)+n
Sn=n(n+1)(2n+1)/6
原式=S(n-1)=n(n-1)(2n-1)/6
相关参考