已知在三角形ABC中,(a-b+c)(sinA+sinB+sinC)=asinC,若b=12,求三角形ABC面積的最大值
已知在三角形ABC中,(a-b+c)(sinA+sinB+sinC)=asinC,若b=12,求三角形ABC面積的最大值
設a/sinA=b/sinB=c/sinC=k,則a=k*sinA,b=k*sinB,c=k*sinC,代入條件等式,得。k*(sinA-sinB+sinC)*(sinA+sinB+sinC)=k*sinA*sinC。(sinA+sinC)^2-sinB*sinB=sinA*sinC。sinA*sinA+sinA*sinC+sinC*sinC=sin(A+C)*sin(A+C)。=sinA*sinA*cosC*cosC+(1/2)*sin2A*cos2C+cosA*cosA*sinC*sinC。2*sinA*sinA*sinC*sinC+sinA*sinC=2sinA*cosA*sinC*cosC。cosA*cosC-sinA*sinC=1/2。cos(A+C)=-cosB=1/2。
導讀設a/sinA=b/sinB=c/sinC=k,則a=k*sinA,b=k*sinB,c=k*sinC,代入條件等式,得。k*(sinA-sinB+sinC)*(sinA+sinB+sinC)=k*sinA*sinC。(sinA+sinC)^2-sinB*sinB=sinA*sinC。sinA*sinA+sinA*sinC+sinC*sinC=sin(A+C)*sin(A+C)。=sinA*sinA*cosC*cosC+(1/2)*sin2A*cos2C+cosA*cosA*sinC*sinC。2*sinA*sinA*sinC*sinC+sinA*sinC=2sinA*cosA*sinC*cosC。cosA*cosC-sinA*sinC=1/2。cos(A+C)=-cosB=1/2。
在三角形ABC中,已知(a-b+c)(sinA+sinB+sinC)=asinC,若b=12,求三角形ABC面積的最大值。設a/sinA=b/sinB=c/sinC=k,則a=k*sinA,b=k*sinB,c=k*sinC,代入條件等式,得:k*(sinA-sinB+sinC)*(sinA+sinB+sinC)=k*sinA*sinC(sinA+sinC)^2-sinB*sinB=sinA*sinCsinA*sinA+sinA*sinC+sinC*sinC=sin(A+C)*sin(A+C)=sinA*sinA*cosC*cosC+(1/2)*sin2A*cos2C+cosA*cosA*sinC*sinC2*sinA*sinA*sinC*sinC+sinA*sinC=2sinA*cosA*sinC*cosCcosA*cosC-sinA*sinC=1/2cos(A+C)=-cosB=1/2cosB=-1/2,sinB=√3/22a*c≤a*a+c*c=b*b+2a*b*cosB=b*b-a*ca*c≤b*b/3=48S△ABC=(1/2)*a*c*sinB≤12*√3第二問AP是什么意思?等腰三角形?根據上述推導,三角形ABC的面積最大值為12*√3。對于第二問,AP的具體含義或條件未明確給出,若考慮等腰三角形的情況,可以進一步探討。
已知在三角形ABC中,(a-b+c)(sinA+sinB+sinC)=asinC,若b=12,求三角形ABC面積的最大值
設a/sinA=b/sinB=c/sinC=k,則a=k*sinA,b=k*sinB,c=k*sinC,代入條件等式,得。k*(sinA-sinB+sinC)*(sinA+sinB+sinC)=k*sinA*sinC。(sinA+sinC)^2-sinB*sinB=sinA*sinC。sinA*sinA+sinA*sinC+sinC*sinC=sin(A+C)*sin(A+C)。=sinA*sinA*cosC*cosC+(1/2)*sin2A*cos2C+cosA*cosA*sinC*sinC。2*sinA*sinA*sinC*sinC+sinA*sinC=2sinA*cosA*sinC*cosC。cosA*cosC-sinA*sinC=1/2。cos(A+C)=-cosB=1/2。
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