^(1/3)<(8-x)(8-x)>+^(1/3)<(27-x)(27-x)>=^(1/3)<(8-x)(27+x)>+7 求x^(1/3)是开立方
问题描述:
^(1/3)<(8-x)(8-x)>+^(1/3)<(27-x)(27-x)>=^(1/3)<(8-x)(27+x)>+7 求x
^(1/3)是开立方
答
原式等价于^(1/3)(8-x)×^(1/3)(8-x)+^(1/3)(27-x)×^(1/3)(27-x)-^(1/3)(8-x)×^(1/3)(27-x)=7其中^(1/3)是开立方,×是乘号令:A=^(1/3)(8-x) B=^(1/3)(27-x) 则有:B×B×B-A×A×A=19(1)式A×A+B×B-A×B=7(...