三角函数¶
函数关系¶
倒数关系¶
- tan\alpha cot\alpha=1
- sin\alpha csc\alpha=1
- cos\alpha sec\alpha=1
商数关系¶
- tan\alpha=\frac{sin\alpha}{cos\alpha}
- cot\alpha=\frac{cos\alpha}{sin\alpha}
平方关系¶
- sin^2\alpha+cos^2\alpha=1
- 1+tan^2\alpha=sec^2\alpha
- 1+cot^2\alpha=csc^2\alpha
诱导公式¶
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和差角公式¶
二角和差公式¶
- sin(\alpha+\beta)=sin\alpha cos\beta+cos\alpha sin\beta
-
sin(\alpha-\beta)=sin\alpha cos\beta-cos\alpha sin\beta
-
cos(\alpha+\beta)=cos\alpha cos\beta-sin\alpha sin\beta
-
cos(\alpha-\beta)=cos\alpha cos\beta+sin\alpha sin\beta
-
tan(\alpha+\beta)=\frac{tan\alpha+tan\beta}{1-tan\alpha tan\beta}
- tan(\alpha-\beta)=\frac{tan\alpha-tan\beta}{1+tan\alpha tan\beta}
和差化积公式¶
- sin\alpha+sin\beta=2sin\frac{\alpha+\beta}{2}cos\frac{\alpha-\beta}{2}
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sin\alpha-sin\beta=2cos\frac{\alpha+\beta}{2}sin\frac{\alpha-\beta}{2}
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cos\alpha+cos\beta=2cos\frac{\alpha+\beta}{2}cos\frac{\alpha-\beta}{2}
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cos\alpha-cos\beta=-2sin\frac{\alpha+\beta}{2}sin\frac{\alpha-\beta}{2}
-
tan\alpha+tan\beta=\frac{sin(\alpha+\beta)}{cos\alpha cos\beta}
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积化和差公式¶
- cos\alpha sin\beta=\frac{1}{2}[sin(\alpha+\beta)-sin(\alpha-\beta)]
- sin\alpha cos\beta=\frac{1}{2}[sin(\alpha+\beta)+sin(\alpha-\beta)]
- cos\alpha cos\beta=\frac{1}{2}[cos(\alpha-\beta)+cos(\alpha+\beta)]
- sin\alpha sin\beta=\frac{1}{2}[cos(\alpha-\beta)-cos(\alpha+\beta)]
倍角公式¶
二倍角公式¶
- sin2\alpha=2sin\alpha cos\alpha=\frac{2tan\alpha}{1+tan^2\alpha}
- cos2\alpha=cos^2\alpha-sin^2\alpha=2cos^2\alpha-1=1-2sin^2\alpha=\frac{1-tan^2\alpha}{1+tan^2\alpha}
- tan2\alpha=\frac{2tan\alpha}{1-tan^2\alpha}
半角公式¶
- sin\frac{\alpha}{2}=\pm\sqrt{\frac{1-cos\alpha}{2}}
- cos\frac{\alpha}{2}=\pm\sqrt{\frac{1+cos\alpha}{2}}
- tan\frac{\alpha}{2}=\frac{sin\alpha}{1+cos\alpha}=\frac{1-cos\alpha}{sin\alpha}=\pm\sqrt{\frac{1-cos\alpha}{1+cos\alpha}}
- cot\frac{\alpha}{2}=\frac{1+cos\alpha}{sin\alpha}=\frac{sin\alpha}{1-cos\alpha}=\pm\sqrt{\frac{1+cos\alpha}{1-cos\alpha}}
正负由 \frac{\alpha}{2} 所在的象限决定
万能公式¶
- sin\alpha=\frac{2tan\frac{\alpha}{2}}{1+tan^2\frac{\alpha}{2}}
- cos\alpha=\frac{1-tan^2\frac{\alpha}{2}}{1+tan^2\frac{\alpha}{2}}
- tan\alpha=\frac{2tan\frac{\alpha}{2}}{1-tan^2\frac{\alpha}{2}}
辅助角公式¶
- asin\alpha+bcos\alpha=\sqrt{a^2+b^2}sin(\alpha+\varphi),tan\varphi=\frac{b}{a}
降幂公式¶
- sin^2\alpha=\frac{1-cos2\alpha}{2}
- cos^2\alpha=\frac{1+cos2\alpha}{2}
- tan^2\alpha=\frac{1-cos2\alpha}{1+cos2\alpha}
正弦定理¶
-
\frac{a}{sinA}=\frac{b}{sinB}=\frac{c}{sinC}=2R
-
S=\frac{1}{2}absinC=\frac{1}{2}acsinB=\frac{1}{2}bcsinA=\frac{abc}{4R}
- a=2RsinA;\ \ \ b=2RsinB;\ \ \ c=2RsinC
- a:b:c=sinA:sinB:sinC
余弦定理¶
- a^2=b^2+c^2-2bccos\alpha
- cosA=\frac{b^2+c^2-a^2}{2bc}