高一数学，最下面这个公式怎么理解，记完的笔记又忘了...
\u9ad8\u4e00\u6570\u5b66\u516c\u5f0f1.\u5f27\u957f\u516c\u5f0f\uff1al=( n\u03c0R/180 )=( aR )\uff0ca\u5706\u5fc3\u89d2\uff0cR\u662f\u534a\u5f84\u3002
2.\u6247\u5f62\u9762\u79ef\u516c\u5f0f\uff1aS=( aR\u5e73\u65b9/2 )=( n\u03c0R\u5e73\u65b9/360 )
3.\u4e09\u89d2\u51fd\u6570\uff1a\u8bbea\u662f\u4e00\u4e2a\u4efb\u610f\u89d2\uff0c\u5728a\u7684\u7ec8\u8fb9\u4e0a\u4efb\u53d6\uff08\u5f02\u4e8e\u539f\u70b9\uff09\u7684\u4e00\u70b9P(x,y)\uff0cP\u4e0e\u539f\u70b9\u7684\u8ddd\u79bbr\uff0c\u5219sinx=( y )/( r );cosx=( x )/( r );tanx=( y )/( x )
4.\u540c\u89d2\u4e09\u89d2\u51fd\u6570\u7684\u5173\u7cfb\uff1a1+tan^2x=( Sec^2x );1+cot^2x=( Cec^2x )
5.\u8bf1\u5bfc\u516c\u5f0f\uff1a
-a \u03c0+a \u03c0-a 2\u03c0-a 2k\u03c0+a \u03c0/2-a \u03c0/2+a 3\u03c0/2-a 3\u03c0/2+a
\u6b63\u5f26 -sina\uff0c-sina , sina\uff0c-sina\uff0csina ,cosa ,cosa,-cosa \uff0c-cosa
\u4f59\u5f26 cosa, -cosa, -cosa, cosa, cosa, sina, -sina,-sina,-sina
\u6b63\u5207 -tana, tana, -tana, -tana, tana, cota\uff0c -cota\uff0ccota\uff0c -cota\uff0c
\u4e09\u89d2\u51fd\u6570\u516c\u5f0f
\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
tan(A+B)=(tanA+tanB)/(1-tanAtanB) tan(A-B)=(tanA-tanB)/(1+tanAtanB)
ctg(A+B)=(ctgActgB-1)/(ctgB+ctgA) ctg(A-B)=(ctgActgB+1)/(ctgB-ctgA)
\u500d\u89d2\u516c\u5f0f
tan2A=2tanA/(1-tan2A) ctg2A=(ctg2A-1)/2ctga
cos2a=cos2a-sin2a=2cos2a-1=1-2sin2a
\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))
ctg(A/2)=\u221a((1+cosA)/((1-cosA)) ctg(A/2)=-\u221a((1+cosA)/((1-cosA))
\u548c\u5dee\u5316\u79ef
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 tanA-tanB=sin(A-B)/cosAcosB
ctgA+ctgBsin(A+B)/sinAsinB -ctgA+ctgBsin(A+B)/sinAsinB
\u67d0\u4e9b\u6570\u5217\u524dn\u9879\u548c
1+2+3+4+5+6+7+8+9+\u2026+n=n(n+1)/2 1+3+5+7+9+11+13+15+\u2026+(2n-1)=n2
2+4+6+8+10+12+14+\u2026+(2n)=n(n+1) 12+22+32+42+52+62+72+82+\u2026+n2=n(n+1)(2n+1)/6
13+23+33+43+53+63+\u2026n3=n2(n+1)2/4 1*2+2*3+3*4+4*5+5*6+6*7+\u2026+n(n+1)=n(n+1)(n+2)/3
\u6b63\u5f26\u5b9a\u7406 a/sinA=b/sinB=c/sinC=2R \u6ce8\uff1a \u5176\u4e2d R \u8868\u793a\u4e09\u89d2\u5f62\u7684\u5916\u63a5\u5706\u534a\u5f84
\u4f59\u5f26\u5b9a\u7406 b2=a2+c2-2accosB \u6ce8\uff1a\u89d2B\u662f\u8fb9a\u548c\u8fb9c\u7684\u5939\u89d2
\u5f27\u957f\u516c\u5f0f l=a*r a\u662f\u5706\u5fc3\u89d2\u7684\u5f27\u5ea6\u6570r >0 \u6247\u5f62\u9762\u79ef\u516c\u5f0f s=1/2*l*r
\u4e58\u6cd5\u4e0e\u56e0\u5f0f\u5206 a2-b2=(a+b)(a-b) a3+b3=(a+b)(a2-ab+b2) a3-b3=(a-b(a2+ab+b2)
\u4e09\u89d2\u4e0d\u7b49\u5f0f |a+b|\u2264|a|+|b| |a-b|\u2264|a|+|b| |a|\u2264b-b\u2264a\u2264b
|a-b|\u2265|a|-|b| -|a|\u2264a\u2264|a|
\u4e00\u5143\u4e8c\u6b21\u65b9\u7a0b\u7684\u89e3 -b+\u221a(b2-4ac)/2a -b-\u221a(b2-4ac)/2a
\u6839\u4e0e\u7cfb\u6570\u7684\u5173\u7cfb X1+X2=-b/a X1*X2=c/a \u6ce8\uff1a\u97e6\u8fbe\u5b9a\u7406
\u5224\u522b\u5f0f
b2-4ac=0 \u6ce8\uff1a\u65b9\u7a0b\u6709\u4e24\u4e2a\u76f8\u7b49\u7684\u5b9e\u6839
b2-4ac>0 \u6ce8\uff1a\u65b9\u7a0b\u6709\u4e24\u4e2a\u4e0d\u7b49\u7684\u5b9e\u6839
b2-4ac<0 \u6ce8\uff1a\u65b9\u7a0b\u6ca1\u6709\u5b9e\u6839\uff0c\u6709\u5171\u8f6d\u590d\u6570\u6839
\u964d\u5e42\u516c\u5f0f
\uff08sin^2\uff09x=1-cos2x/2
\uff08cos^2\uff09x=i=cos2x/2
\u4e07\u80fd\u516c\u5f0f
\u4ee4tan(a/2)=t
sina=2t/(1+t^2)
cosa=(1-t^2)/(1+t^2)
tana=2t/(1-t^2)
换元思想
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