Question

已知x-1/x=5,求（1）x²+1/x²；（2）x四次方+1/x四次方（3）x²-5x-

Answer 1

(1)

x-1/x=5 平方一下

x^2-2+1/x^2=25

x^2+1/x^2=25+2=27

(2)

x^2+1/x^2=27 平方一下

x^4+2+1/x^4=729

x^4+1/x^4=729-2=727

(3)

x-1/x=5

x^2-1=5x

x^2-5x=1

x^2-5x-7

=1-7

=-6