为什么-（-x）sin（-x）=-sinx sin(x+π）=-sinx对吗
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sin(-a)=-sin(a)
sin(\u03c02-a)=cos(a)
cos(\u03c02-a)=sin(a)
sin(\u03c02+a)=cos(a)
cos(\u03c02+a)=-sin(a)
sin(\u03c0-a)=sin(a)
sin(\u03c0+a)=-sin(a)
tgA=tanA=sinAcosA
2\u3001\u4e24\u89d2\u548c\u516c\u5f0f
sin(a+b)=sinacosb+cosasinb
sin(a-b)=sinacosb-sinbcosa
cos(a+b)=cosacosb-sinasinb
cos(a-b)=cosacosb+sinasinb
3\u3001\u500d\u89d2\u516c\u5f0f
tan2a=2tana/[1-(tana)^2]
cos2a=(cosa)^2-(sina)^2=2(cosa)^2 -1=1-2(sina)^2
sin2a=2sina*cosa
4\u3001\u534a\u89d2\u516c\u5f0f
sin(a/2)=\u221a((1-cosa)/2) sin(a/2)=-\u221a((1-cosa)/2)
cos(a/2)=\u221a((1+cosa)/2) cos(a/2)=-\u221a((1+cosa)/2)
tan(a/2)=\u221a((1-cosa)/((1+cosa)) tan(a/2)=-\u221a((1-cosa)/((1+cosa))
cot(a/2)=\u221a((1+cosa)/((1-cosa)) cot(a/2)=-\u221a((1+cosa)/((1-cosa))
tan(a/2)=(1-cosa)/sina=sina/(1+cosa)
5\u3001\u548c\u5dee\u5316\u79ef\u516c\u5f0f
2sinacosb=sin(a+b)+sin(a-b)
2cosasinb=sin(a+b)-sin(a-b) )
2cosacosb=cos(a+b)-sin(a-b)
-2sinasinb=cos(a+b)-cos(a-b)
sina+sinb=2sin((a+b)/2)cos((a-b)/2
cosa+cosb=2cos((a+b)/2)sin((a-b)/2)
tana+tanb=sin(a+b)/cosacosb
6\u3001\u79ef\u5316\u548c\u5dee\u516c\u5f0f
sin(a)sin(b)=-1/2*[cos(a+b)-cos(a-b)]
cos(a)cos(b)=1/2*[cos(a+b)+cos(a-b)]
sin(a)cos(b)=1/2*[sin(a+b)+sin(a-b)]
7\u3001\u8bf1\u5bfc\u516c\u5f0f
sin(-a)=-sin(a)
cos(-a)=cos(a)
sin(pi/2-a)=cos(a)
cos(pi/2-a)=sin(a)
sin(pi/2+a)=cos(a)
cos(pi/2+a)=-sin(a)
sin(pi-a)=sin(a)
cos(pi-a)=-cos(a)
sin(pi+a)=-sin(a)
cos(pi+a)=-cos(a)
tga=tana=sina/cosa
8\u3001\u4e07\u80fd\u516c\u5f0f
sin(a)= (2tan(a/2))/(1+tan^2(a/2))
cos(a)= (1-tan^2(a/2))/(1+tan^2(a/2))
tan(a)= (2tan(a/2))/(1-tan^2(a/2))
9\u3001\u5176\u5b83\u516c\u5f0f
a*sin(a)+b*cos(a)=sqrt(a^2+b^2)sin(a+c) [\u5176\u4e2d,tan(c)=b/a]
a*sin(a)-b*cos(a)=sqrt(a^2+b^2)cos(a-c) [\u5176\u4e2d,tan(c)=a/b]
1+sin(a)=(sin(a/2)+cos(a/2))^2
1-sin(a)=(sin(a/2)-cos(a/2))^2
10\u3001\u5176\u4ed6\u975e\u91cd\u70b9\u4e09\u89d2\u51fd\u6570
csc(a)=1/sin(a)
sec(a)=1/cos(a)
11\u3001\u53cc\u66f2\u51fd\u6570
sinh(a)=(e^a-e^(-a))/2
cosh(a)=(e^a+e^(-a))/2
tgh(a)=sinh(a)/cosh(a)
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由诱导公式，sin（-x）=-sinx
所以 ， -（-x）sin（-x）=X(-sinx)=-Xsinx
-(-X)SIN(-X)
=XSIN(-X)
=-XSINX
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