sin^2 a＊tana＋cos^2＊cota＋2sina＊cosa＝sin^2 a*sin a/cosa+cos^2a*cosa/sin a+2sina*cosa=(sin^4 a+cos^4a)/sina*cosa+2sina*cosa=(sin^2 a+cos^2a)^2/sina*cosa-2sina*cosa+2sina*cosa=1/sina*cosa=2/sin2a...