3个简单的数学三角函数题!
1.在三角形ABC中,sinA=sinB+sinC/cosB+cosC.判断三角形的形状.
2.四边形ABCD中,AD垂直于CD,AD=10.AB=14∠BDA=60°∠BCD=135°
求BC长.
3.三角形ABC中,C=2A,a+c=10,cosA=3/4求b.
任和回答:
1.sinA=(sinB+sinC)/(cosB+cosC)sin(B+C)=(sinB+sinC)/(cosB+cosC)sinBcosC+cosBsinC=(sinB+sinC)/(cosB+cosC)sinBcosBcosC+sinB(cosC)^2+(cosB)^2sinC+cosBsinCcosC=sinB+sinCsinBcosBcosC+cosBsinCcosC=sinB-s...
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