推 ArzasV :做圖畫四邊形 考慮斜率 06/05 00:24
※ 引述《adamchi (adamchi)》之銘言:
: 1.若0<x<1,且x+1/x=3
: 求x^3 - 1/(x^3) = ?
: 答:-8*5^(1/2)
x+1/x=3 ==> x^2 + 2 +(1/x^2)=9
x^2+(1/x^2)=7
x^2+(1/x^2)-2 =5
(x-1/x)^2 =5
(x-1/x) = ±√5 (正不和) -√5
x^3 - 1/(x^3) = (x-1/x)(x^2 +1+1/x^2) =-√5 *8 = -8√5
: 2.已知某個線性函數f(x)= ax+b (a不等於0)
: 1<f(1)<7 , 2<f(2)<5
: 試求f(5)的範圍為_______
: 請問該兩題怎麼算,謝謝~
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