(sinx^2+sin2x)/(cosx^2=cos2x)等于多少

(sinx^2+sin2x)/(cosx^2=cos2x)等于多少
(sinx^2+sin2x)/(cosx^2=cos2x)等于多少

 

(sinx^2+sin2x)/(cosx^2=cos2x)等于多少
(1)根据图信息可知
sina=4/5 cosa=3/5
∴(sina^2+sin2a)/(cosa^2+cos2a)=(sina^2+2sinacosa)/(cosa^2+cosa^2-sina^2)
=(16/25+2*3/5*4/5)/(2*9/25-16/25)=20.
(2)cos(∠COB)=cos(a+60)=1/2cosa-sina*√3/2=1/2*3/5-4/5*√3/2=(3-4√3)/10

(1)
根据题意: sin(a) = 4/5, cos(a) = 3/5
sin(2a) = 2sin(a)cos(a) = 24/25
cos(2a) = cos(a)cos(a) - sin(a)sin(a) = -7/25
原式 = (16/25 + 24/25) / (9/25 - 7/25) = 20
(2)
cos(COB) = cos(a+60) = cos(a)cos(60)-sin(a)sin(60) = (3-4√3)/10

sin2x=2sinx*cosx; cos2x=cosx*cosx-sinx*sinx sin2x=2sinxcosx不等于2sinx cos2x=2cos^2（x）-1不等于2cosx