1.已知α是第二象限角,f(α)=[sin(3π/2-α)·cos(2π-α)·tan(π-α)]/-cos(-π-α).
(1)化简f(α)
(2)若sin(π/2 -α)=-½,求f(α)的值.
2.若π/2＜α＜π,化简√(1/2+1/2√1/2+1/2cos2α)
3.已知0＜α＜（π/4）,0＜β＜（π/4）,且3sinβ=sin(2α+β),4tan(α/2)=1-tan²(α/2),求α+β的值.
我数学很不好,遇见这种题没有思路,