ömer_hoca'den alıntı
Şevval, a=95 olduğunu farzedelim tan2a negatif midir?
sinα.cosα-cos²α=(1/2)[2sinacosa]-(1/2)[cos2a+1]=(1/2)[sin2a-cos2a-1]
(pi/2)<a<(pi) ve tan2a > 0 => sin2a<0 ve cos2a<0
tan2a=3/4 => sin2a=-(4/5) cos2a=-(3/5)
sinα.cosα-cos²α=(1/2)[2sinacosa]-(1/2)[cos2a+1]=(1/2)[sin2a-cos2a-1]=(1/2)[-(4/5)+(3/5)-(5/5)]=-(3/5)