cos2x等于多少 cos2x等于什么??
Cos2x\u7b49\u4e8e\u4ec0\u4e48\uff1f\u4e09\u89d2\u51fd\u6570\u4ee3\u6362\uff1a
cos2X=(cosX)^2-(sinX)^2=2*(cosX)^2-1=1-2*(sinX)^2
\u5373\uff1acos2x=2cosx\u7684\u5e73\u65b9-1=cosx\u7684\u5e73\u65b9-sinx\u5e73\u65b9=1-2sinx\u7684\u5e73\u65b9
cos2x\u7684\u51fd\u6570\u56fe\u50cf:
\u6269\u5c55\u8d44\u6599\uff1a
\u5e38\u7528\u516c\u5f0f\uff1a
\u516c\u5f0f\u4e00\uff1a
\u8bbe\u03b1\u4e3a\u4efb\u610f\u89d2\uff0c\u7ec8\u8fb9\u76f8\u540c\u7684\u89d2\u7684\u540c\u4e00\u4e09\u89d2\u51fd\u6570\u7684\u503c\u76f8\u7b49\uff1a
sin\uff082k\u03c0+\u03b1\uff09=sin\u03b1 \uff08k\u2208Z\uff09
cos\uff082k\u03c0+\u03b1\uff09=cos\u03b1 \uff08k\u2208Z\uff09
tan\uff082k\u03c0+\u03b1\uff09=tan\u03b1 \uff08k\u2208Z\uff09
cot\uff082k\u03c0+\u03b1\uff09=cot\u03b1\uff08k\u2208Z\uff09
\u516c\u5f0f\u4e8c\uff1a
\u8bbe\u03b1\u4e3a\u4efb\u610f\u89d2\uff0c\u03c0+\u03b1\u7684\u4e09\u89d2\u51fd\u6570\u503c\u4e0e\u03b1\u7684\u4e09\u89d2\u51fd\u6570\u503c\u4e4b\u95f4\u7684\u5173\u7cfb\uff1a
sin\uff08\u03c0+\u03b1\uff09= \uff0dsin\u03b1
cos\uff08\u03c0+\u03b1\uff09=\uff0dcos\u03b1
tan\uff08\u03c0+\u03b1\uff09= tan\u03b1
cot\uff08\u03c0+\u03b1\uff09=cot\u03b1
\u516c\u5f0f\u4e09\uff1a
\u4efb\u610f\u89d2\u03b1\u4e0e-\u03b1\u7684\u4e09\u89d2\u51fd\u6570\u503c\u4e4b\u95f4\u7684\u5173\u7cfb\uff08\u5229\u7528 \u539f\u51fd\u6570 \u5947\u5076\u6027\uff09\uff1a
sin\uff08\uff0d\u03b1\uff09=\uff0dsin\u03b1
cos\uff08\uff0d\u03b1\uff09= cos\u03b1
tan\uff08\uff0d\u03b1\uff09=\uff0dtan\u03b1
\u516c\u5f0f\u56db\uff1a
\u5229\u7528\u516c\u5f0f\u4e8c\u548c\u516c\u5f0f\u4e09\u53ef\u4ee5\u5f97\u5230\u03c0-\u03b1\u4e0e\u03b1\u7684\u4e09\u89d2\u51fd\u6570\u503c\u4e4b\u95f4\u7684\u5173\u7cfb\uff1a
sin\uff08\u03c0\uff0d\u03b1\uff09= sin\u03b1
cos\uff08\u03c0\uff0d\u03b1\uff09=\uff0dcos\u03b1
tan\uff08\u03c0\uff0d\u03b1\uff09=\uff0dtan\u03b1
cot\uff08\u03c0\uff0d\u03b1\uff09=\uff0dcot\u03b1
\u516c\u5f0f\u4e94\uff1a
\u5229\u7528\u516c\u5f0f\u4e00\u548c\u516c\u5f0f\u4e09\u53ef\u4ee5\u5f97\u52302\u03c0-\u03b1\u4e0e\u03b1\u7684\u4e09\u89d2\u51fd\u6570\u503c\u4e4b\u95f4\u7684\u5173\u7cfb\uff1a
sin\uff082\u03c0-\u03b1\uff09= \uff0dsin\u03b1
cos\uff082\u03c0-\u03b1\uff09= cos\u03b1
tan\uff082\u03c0-\u03b1\uff09=\uff0dtan\u03b1
cot\uff082\u03c0-\u03b1\uff09=\uff0dcot\u03b1
\u516c\u5f0f\u516d\uff1a
\u03c0/2\u00b1\u03b1\u4e0e\u03b1\u7684\u4e09\u89d2\u51fd\u6570\u503c\u4e4b\u95f4\u7684\u5173\u7cfb\uff1a
sin\uff08\u03c0/2+\u03b1\uff09=cos\u03b1
sin\uff08\u03c0/2\uff0d\u03b1\uff09=cos\u03b1
cos\uff08\u03c0/2+\u03b1\uff09=\uff0dsin\u03b1
cos\uff08\u03c0/2\uff0d\u03b1\uff09=sin\u03b1
tan\uff08\u03c0/2+\u03b1\uff09=\uff0dcot\u03b1
tan\uff08\u03c0/2\uff0d\u03b1\uff09=cot\u03b1
cot\uff08\u03c0/2+\u03b1\uff09=\uff0dtan\u03b1
cot\uff08\u03c0/2\uff0d\u03b1\uff09=tan\u03b1
\u63a8\u7b97\u516c\u5f0f\uff1a
3\u03c0/2 \u00b1 \u03b1\u4e0e\u03b1\u7684\u4e09\u89d2\u51fd\u6570\u503c\u4e4b\u95f4\u7684\u5173\u7cfb\uff1a
sin\uff083\u03c0/2+\u03b1\uff09=\uff0dcos\u03b1
sin\uff083\u03c0/2\uff0d\u03b1\uff09=\uff0dcos\u03b1
cos\uff083\u03c0/2+\u03b1\uff09=sin\u03b1
cos\uff083\u03c0/2\uff0d\u03b1\uff09=\uff0dsin\u03b1
tan\uff083\u03c0/2+\u03b1\uff09=\uff0dcot\u03b1
tan\uff083\u03c0/2\uff0d\u03b1\uff09=cot\u03b1
cot\uff083\u03c0/2+\u03b1\uff09=\uff0dtan\u03b1
cot\uff083\u03c0/2\uff0d\u03b1\uff09=tan\u03b1
\u53c2\u8003\u8d44\u6599\uff1a\u4e09\u89d2\u51fd\u6570\u8bf1\u5bfc\u516c\u5f0f\u767e\u5ea6\u767e\u79d1
\u89e3\uff1acos2x=cos(x+x)
=cosx*cosx-sinx*sinx
=(cosx)^2-(sinx)^2
\u53c8\u56e0\u4e3a1=(sinx)^2+(cosx)^2
\u6240\u4ee5\uff0c
(cosx)^2-(sinx)^2=2(cosx)^2-1=1-2(sinx)^2
\u5373cos2x=2(cosx)^2-1=1-2(sinx)^2\u3002
\u6269\u5c55\u8d44\u6599\uff1a
1\u3001\u4e09\u89d2\u51fd\u6570\u4e24\u89d2\u548c\u5dee\u516c\u5f0f
\uff081\uff09sin(A+B)=sinAcosB+cosAsinB
\uff082\uff09sin(A-B)=sinAcosB-cosAsinB
\uff083\uff09cos(A+B)=cosAcosB-sinAsinB
\uff084\uff09cos(A-B)=cosAcosB+sinAsinB
2\u3001\u4e09\u89d2\u51fd\u6570\u7684\u4e8c\u500d\u89d2\u516c\u5f0f
\uff081\uff09sin2A=sin(A+A)=sinAcosA+cosAsinA=2sinAcosA
\uff082\uff09cos2A==cos(A+A)=(cosA)^2-(sinA)^2=2(cosA)^2-1=1-2(sinA)^2
\u53c2\u8003\u8d44\u6599\u6765\u6e90\uff1a\u767e\u5ea6\u767e\u79d1-\u4e09\u89d2\u51fd\u6570\u516c\u5f0f
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