先化简,再求值:【2x+y】的2次方-【2x-y】【2x+y】-4xy,其中x=2013,y=-1.123的2次方-124乘122若a+1/a=5,则a-1/a=( )
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![先化简,再求值:【2x+y】的2次方-【2x-y】【2x+y】-4xy,其中x=2013,y=-1.123的2次方-124乘122若a+1/a=5,则a-1/a=( )](/uploads/image/z/5238011-11-1.jpg?t=%E5%85%88%E5%8C%96%E7%AE%80%2C%E5%86%8D%E6%B1%82%E5%80%BC%EF%BC%9A%E3%80%902x%2By%E3%80%91%E7%9A%842%E6%AC%A1%E6%96%B9-%E3%80%902x-y%E3%80%91%E3%80%902x%2By%E3%80%91-4xy%2C%E5%85%B6%E4%B8%ADx%3D2013%2Cy%3D-1.123%E7%9A%842%E6%AC%A1%E6%96%B9-124%E4%B9%98122%E8%8B%A5a%2B1%2Fa%3D5%2C%E5%88%99a-1%2Fa%3D%EF%BC%88+%EF%BC%89)
先化简,再求值:【2x+y】的2次方-【2x-y】【2x+y】-4xy,其中x=2013,y=-1.123的2次方-124乘122若a+1/a=5,则a-1/a=( )
先化简,再求值:【2x+y】的2次方-【2x-y】【2x+y】-4xy,其中x=2013,y=-1.
123的2次方-124乘122
若a+1/a=5,则a-1/a=( )
先化简,再求值:【2x+y】的2次方-【2x-y】【2x+y】-4xy,其中x=2013,y=-1.123的2次方-124乘122若a+1/a=5,则a-1/a=( )
【2x+y】的2次方-【2x-y】【2x+y】-4xy,其中x=2013,y=-1.
=(2x+y)(2x+y-2x+y)-4xy
=4xy+2y²-4xy
=2y²
=2*(-1)²
=2
123的2次方-124乘122
=123²-(123+1)(123-1)
=123²-123²+1
=1
若a+1/a=5,则a-1/a=(±√21 )
(2x+y)²-(2x-y)(2x+y)-4xy
=(2x+y)(2x+y-2x+y)-4xy
=4xy+2y²-4xy
=2y²
将y=-1代入上式则
原式=2
123²-124×122
=123²-(123+1)(123-1)
=123²-123²+...
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(2x+y)²-(2x-y)(2x+y)-4xy
=(2x+y)(2x+y-2x+y)-4xy
=4xy+2y²-4xy
=2y²
将y=-1代入上式则
原式=2
123²-124×122
=123²-(123+1)(123-1)
=123²-123²+1
=1
a+1/a=5
两边同时平方
a² +1/a² +2=25
a² +1/a² =23
a² +1/a² -2=23-2=21
(a - 1/a)² =21
a-1/a =±√21
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