GWD5-7

[Emilyh]

Q7:
√[2√63 + 2/(8+3√7)] =

A. 8 + 3√7
B. 4 + 3√7
C. 8
D. 4
E. √7
Answer: D

請問這題要如何做?

謝謝

[FrankChang]

√[2√63 + 2/(8+3√7)] =√{6√7 + 2(8-3√7)/[(8+3√7)(8-3√7)]}
=√[6√7 + (16-6√7)/(64-63)]=√16=4