Question

已知x²+y²=4,则的最小值为

A.－2                                                             B.－

C.2－2                                                      D.2+2

Answer 1

C

解析:

设x=2cosθ,y=2sinθ,

则=.

设sinθ+cosθ=t,则

－≤t≤,且sinθcosθ=.

∴==2(t+1)∈［2－2,2+2］.