已知sin2a=1/3,且π/4A.2√3/3 B.-2√3/3 C.3/4 D.-3/4(需要详细步骤)

问题描述:

已知sin2a=1/3,且π/4
A.2√3/3 B.-2√3/3 C.3/4 D.-3/4(需要详细步骤)