已知x+y=12,xy=9,且x
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已知x+y=12,xy=9,且x 已知x+y=12,xy=9,且x (x^1/2-y^1/2)/(x^1/2+y^1/2) 分母有理化=(x^1/2-y^1/2)^2/(x-y) =(x+y-2x^1/2y^1/2)/(x-y) =(12-2*3)/(x-y)=6/(x-y) x-y=-[(x-y)^2]^1/2 (此处取负号imqu因为x〈y) =-[... 全部展开 (x^1/2-y^1/2)/(x^1/2+y^1/2) 分母有理化=(x^1/2-y^1/2)^2/(x-y) =(x+y-2x^1/2y^1/2)/(x-y) =(12-2*3)/(x-y)=6/(x-y) x-y=-[(x-y)^2]^1/2 (此处取负号imqu因为x〈y) =-[(x+y)^2-4xy]^1/2 =-(12^2-4*9)^1/2 =-6根号3 所以(x^1/2-y^1/2)/(x^1/2+y^1/2) =-1/根号3有不懂的可以追问哦 收起
已知x+y=12,xy=9,且x
x+y=12,xy=9
(1)x的二分之一次方+y的二分之一次方
=√x+√y=√(√x+√y)^2=√(x+y+2√xy)=√(12+2√9)=√18=3√2
(2) x的二分之一次方-y的二分之一次
=√x-√y=√(√x-√y)^2=√(x+y-2√xy)=√(12-2√9)=√6