S=3/根号7-2,化简得S=根号7+2.为什么

问题描述:

S=3/根号7-2,化简得S=根号7+2.为什么

s=3(√7+2)/[(√7+2)(√7-2)]
=3(√7+2)/(7-4)
=3(√7+2)/3
=√7+2