由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a

来源：学生作业帮编辑：作业帮分类：数学作业时间：2024/05/14 07:02:14

由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a sin b解题
设a为锐角,证：
1、2分之根3乘cos a + 2分之1乘sin a=cos(6分之π-a)
2、cos a-sin a=根号2cos(4分之π+a)

√3/2*cos a + 1/2*sin a
=cosπ/6*cos a + sinπ/6sin a
=cos(π/6- a)
cos a-sin a
=√2(√2/2cos a-√2/2sin a)
=√2(cosπ/4*cos a - sinπ/4sin a)
=√2cos(π/4+ a )

由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明求证:cos(a+b)cos(a-b)=cos平方b-sin平方a cos(a-b)cos(b-c)+sin(a-b)sin(b-c)= cos^B-cos^C=sin^A,三角形的形状若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2 证明cos(a+b)=cos(a)cos(b)-sin(a)sin(b)详细步骤,书上的证明看不懂. cosb=cos[(a+b)-a]=cos(a+b)cosa+sin(a+b)sina cos(a+b)+cos(a-b)/sin(a+b)+sin(a-b)化简 sin²(a+b)+cos²(a+b)= sin(a)*cos(a)=4,那么sin(a) cos(b)=?