杭州交通信息网综漫之铃科百合子:2道初一的数学题,学过的就会做!!!1
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2.已知a+a^-1=3.求(1)a^2+a^-2 (2)a^-3+b^-3
(3)a^4+a^-4
1. X^2 + 1/16 + X/2 - (X^2 - 1/16) = 1/4
X/2 + 1/8 = 1/4
X = 1/4
2. a + 1/a = 3
(1) a^2 + a^-2 =(a + 1/a)^2 - 2
=9 - 2
=7
(2) a^3 + a^-3 =(a + 1/a)*(a^2 + a^-2 - 1)
=3 * (7-1)
=18
(3) a^4 + a^-4 = (a^2 + a^-2)^2 - 2
= 49 -2
=47
1. (x+1/4)^2-(x+1/4)*(x-1/4)=1/4
(x+1/4)[(x+1/4) - (x-1/4)]=1/4
(x+1/4)*1/2=1/4
x+1/4=1/2
x=1/4
2.
1).a^2+a^-2
=(a+a^-1)^2 - 2
=3^2 -2
=7
2).a^3+a^-3
=(a+a^-1)(a^2 - a*a^-1 + a^-2)
=3*(7-1)
=18
个人认为第二题要改正一下！！！
3).a^4+a^-4
=(a^2+a^-2)^2 -2
=7^2 -2
=47
1. X^2 + 1/16 + X/2 - (X^2 - 1/16) = 1/4
X/2 + 1/8 = 1/4
X = 1/4
2. a + 1/a = 3
(1) a^2 + a^-2 =(a + 1/a)^2 - 2
=9 - 2
=7
(2) a^3 + a^-3 =(a + 1/a)*(a^2 + a^-2 - 1)
=3 * (7-1)
=18
(3) a^4 + a^-4 = (a^2 + a^-2)^2 - 2
= 49 -2
=47