已知角α顶点在原点,始边在x轴正半轴上,终边经过点P(1,-2)求sinα,cosα,tan2α的值

问题描述:

已知角α顶点在原点,始边在x轴正半轴上,终边经过点P(1,-2)
求sinα,cosα,tan2α的值

sinα= -2/5-²
cosα= 1/5-²
tan2α= 4/3

sina=y/r=-2/(1^2+(-2)^2)^0.5=-2/5^0.5
cosa=x/r=1/5^0.5
tan2a=sin2a/cos2a=2sinacosa/(2(cosa)^2-1)
=4/3