证明sin(a+b)sin(a-b)=sin²a-sin² b,并用该式计算sin²20°+sin80°sin40°
来源：学生作业帮助网 编辑：六六作业网 时间：2024/12/23 12:57:57
证明sin(a+b)sin(a-b)=sin²a-sin²b,并用该式计算sin²20°+sin80°sin40°证明sin(a+b)sin(a-b)=sin²
证明sin(a+b)sin(a-b)=sin²a-sin² b,并用该式计算sin²20°+sin80°sin40°
证明sin(a+b)sin(a-b)=sin²a-sin² b,并用该式计算sin²20°+sin80°sin40°
证明sin(a+b)sin(a-b)=sin²a-sin² b,并用该式计算sin²20°+sin80°sin40°
sin(a+b)sin(a-b)
=(sinacosb+sinbcosa)(sinacosb-sinbcosa)
=(sinacosb)^2+sinasinbcosacosb-sinasinbcosacosb-(sinbcosa)^2
=(sinacosb)^2-(1-sin^2a)(1-cos^2b)
=(sinacosb)^2-[1-sin^2a-cos^2b+(sinacosb)^2]
=-1+sin^2a+(1-sin^2b)
=sin^2 a-sin^2 b
sin²20°+sin80°sin40°
=sin²20°+sin(60°+20°)sin(60°-20°)
=sin²20°+sin²60°-sin²20°
=sin²60°
=(√3/2)²
=3/4
证明sin(a+b)sin(a-b)=sin^2 a-sin^2 b,
如何证明sin(a+b)sin(a-b)=sin*a-sin*b (*为平方)
【证明】Sin A+sin B=2Sin 22
怎样证明/sin a +sin b/
证明sina sin(a+2b) - sinb sin(b+2a) =sin(a+b)sin(a-b)
如何证明sin(a+b)=sin(a)cos(b)+cos(α)sin(b)
懂得进.证明,sina+sin(a+b)+sin(a+2b)+...sin(a+nb)=sin(a+ab/2)sin[(n+1)b/2]/sin(b/2)
证明sin(a+b)=sinacosb+cosasinb
证明sin(A+B)=sinAcosB+cosAsinB
证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2B=1
用正弦定理证明a+b/c=sin A+sin B/sin c
证明sin(A+B)sin(A-B)=cos^2B-cos^2A
证明 sin(A+B)cos(A-B)=sinAcosA+sinBcosB
证明三角函数等式sin(A+B)-sinA=2cos(A+B/2)sin(B/2)
证明sin(a+b)sin(a-b)=sin²a-sin² b,并用该式计算sin²20°+sin80°sin40°
证明 SIN²A+SIN²B-SIN²C=2SINASINBCOSC
cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 用三角形证明我 已经证明了sin(a+b)=sin(a)*cos(b)+cos(a)*sin(b) 用 三角形证明 了过程如下： 现在跪求希望大家帮我证明：cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b) 也用 三角形证明 .
如何证明sinA2-sinB2=sin(A-B)*sin(A+B)