初二数学三角函数公式
<p> 两角和公式</p><p>sin(A+B)=sinAcosB+cosAsinBsin(A-B)=sinAcosB-sinBcosA</p><p>cos(A+B)=cosAcosB-sinAsinBcos(A-B)=cosAcosB+sinAsinB</p><p>tan(A+B)=(tanA+tanB)/(1-tanAtanB)tan(A-B)=(tanA-tanB)/(1+tanAtanB)</p><p>ctg(A+B)=(ctgActgB-1)/(ctgB+ctgA)ctg(A-B)=(ctgActgB+1)/(ctgB-ctgA)</p><p>倍角公式</p><p>tan2A=2tanA/(1-tan2A)ctg2A=(ctg2A-1)/2ctga</p><p>cos2a=cos2a-sin2a=2cos2a-1=1-2sin2a</p><p>半角公式</p><p>sin(A/2)=√((1-cosA)/2)sin(A/2)=-√((1-cosA)/2)</p><p>cos(A/2)=√((1+cosA)/2)cos(A/2)=-√((1+cosA)/2)</p><p>tan(A/2)=√((1-cosA)/((1+cosA))tan(A/2)=-√((1-cosA)/((1+cosA))</p><p>ctg(A/2)=√((1+cosA)/((1-cosA))ctg(A/2)=-√((1+cosA)/((1-cosA))</p><p>和差化积</p><p>2sinAcosB=sin(A+B)+sin(A-B)2cosAsinB=sin(A+B)-sin(A-B)</p><p>2cosAcosB=cos(A+B)-sin(A-B)-2sinAsinB=cos(A+B)-cos(A-B)</p><p>sinA+sinB=2sin((A+B)/2)cos((A-B)/2</p><p>cosA+cosB=2cos((A+B)/2)sin((A-B)/2)</p><p>tanA+tanB=sin(A+B)/cosAcosBtanA-tanB=sin(A-B)/cosAcosB</p><p>ctgA+ctgBsin(A+B)/sinAsinB-ctgA+ctgBsin(A+B)/sinAsinB</p>
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