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+
3

=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-
2
+
2

=-3;

(2)原方程两边同乘以(x-3)可化为:2-x+3(x-3)=-2
2x=5
x=

5
2


经检验x=

5
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

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