已知sina+cosa=p,求(1)sina*cosa(2)sin^2a-cos^2a(3)sin^3a+-cos^3a(4)sin^4a+-ctg^3a
问题描述:
已知sina+cosa=p,求(1)sina*cosa(2)sin^2a-cos^2a(3)sin^3a+-cos^3a(4)sin^4a+-ctg^3a
答
sina+cosa=p(1)(sina+cosa)²=sin²a+2sina·cosa+cos²a=1+2sina·cosa=p²sina·cosa=(p²-1)/2(2)(sina-cosa)²=sin²a-2sina·cosa+cos²a=1-2sina·cosa=1-(p²-1)=2-p&su...