作业帮若x^?+x^-?=9,则x^2+1/x^2=?若x^?-x^-?=3,则x^2+1/x^2=?
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若x^?+x^-?=9,则x^2+1/x^2=?若x^?-x^-?=3,则x^2+1/x^2=?
我打错了，应是若x^1/2+x^-1/2=9,则x^2+1/x^2=?
若x^1/2-x^-1/2=3,则x^2+1/x^2=?
我打错了，应是若x^1/2+x^-1/2=9,则x^2+1/x^2=?
若x^1/2-x^-1/2=3,则x^2+1/x^2=?
这就看你对问题的把握了,应定要仔细观察题目已知与未知的联系.本题中已知为一次,未知为二次,正好通过平方求得,
x^(1/2)+x^(-1/2)=9
x^2+1/x^2
=(x+1/x)^2-2
=[(x^(1/2)+x^(-1/2)^2-2]^2-2
=(81-2)^2-2
=6
会了第一个,第二个应该也会了吧,这是两次平方而已
x^(1/2)-x^(1/2)=3
x^2+1/x^2
=(x-1/x)^2+2
=[(x^(1/2)-x^(-1/2))^2+2]^2+2
=(3^2+2)^2+2
=121+2
=123
x^(1/2)+x^(-1/2)=9
x^2+1/x^2
=(x+1/x)^2-2
=[(x^(1/2)+x^(-1/2)^2-2]^2-2
=(81-2)^2-2
=6
会了第一个,第二个应该也会了吧,这是两次平方而已
x^(1/2)-x^(1/2)=3
x^2+1/x^2
=(x-1/x)^2+2
=[(x^(1/2)-x^(-1/2))^2+2]^2+2
=(3^2+2)^2+2
=121+2
=123
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