sinb

“sinB”的意思：角B的正弦是多少。在直角三角形中，∠B（非直角）的对边与斜边的比叫做∠B的正弦，记作sinB。正弦定理（The Law of Sines...

sinB=sin(120°-arcsinB)= sin120°cosarcsinB-cos120°sinarcsinB= √3/2 * √{1-(4√3/7)²} + 1/2*4√3/7= √3/2...

sin(a-b)=sina*cosb-cosa*sinb我们把两式相加就得到sin(a+b)+sin(a-b)=2sina*cosb所以,sina*cosb=(sin(a+b)+sin(a-b))/2同理...

sinB+sinC=sinB+sin(120°-B)=sinB+(根号3)/2coxB+1/2sinB=3/2sinB+(根号3)/2cosB=(根号3)sin(B+30°)∵B∈(0°,120°),sin(B+30°)∈(1/2,1],...

解答:解:当A=0,B=π时,满足sinA=sinB=0,但A=B不成立.若A=B,则sinA=sinB成立,∴“sinA=sinB”是“A=B”的必要不充分条件,故选:B.

1、Sin(A+B)=SinA*CosB+SinB*CosA 2、Sin(A-B)=SinA*CosB-SinB*CosA 3、Cos(A+B)=CosA*CosB-SinA*SinB 4、Cos(A-B)=CosA*CosB+SinA*SinB 5、Tan(A+B)...

b = t·sinB c = t·sin(60° - B/2) a = t·sin(120° - B/2) 又因为 a + c = 2b 带进去就是: t·sin(120° - B/2) + t·sin(60° - B/2) = ...

解:由余弦定理得:a^2=b^2+c^2-2bccosA=7^2 b^2+c^2+bc=49 ---(1) (cosA=cos120°=-1/2)b+c=8(b+c)^2=64b^2+c^2+2bc=64 ---(2)(2)-(...

解答:证明:在△ABC中,设BC=a,AC=b,AB=c.作CH⊥AB垂足为点H,∵CH=a sinB,CH=b sinA,∴a sinB=b sinA,得到asinA=bsinB,同理,在△ABC中,bsinB=csinC,∵同弧...