sin(2011兀/2-2a)已知sina+2cosa=0.求原式值

问题描述:

sin(2011兀/2-2a)已知sina+2cosa=0.求原式值

sina+2cosa=0=> tana=sina/cosa=-2
所以
sin(2011π/2 - 2a)
=sin(3π/2-2a)
=-cos2a
=1-2(cosa)²
=1-2/(seca)²
=1-2/[1+(tana)²]
=1-2/5
=3/5