Sách lượng giác/Công thức lượng giác/Đẳng thức lượng giác nghịch

$\arcsin (x)+\arccos (x)=\pi /2$

$\arctan (x)+\mathrm{arccot}(x)=\pi /2.$

$\arctan (x)+\arctan (1/x)=\{\begin{array}{cc}\pi /2,& \text{n}\acute{\hat{\text{e}}}\text{u}x>0\\ -\pi /2,& \text{n}\acute{\hat{\text{e}}}\text{u}x<0\end{array}.$

$\arctan (x)+\arctan (y)=\arctan \left(\frac{x+y}{1-xy}\right)$

$\arctan (x)-\arctan (y)=\arctan \left(\frac{x-y}{1+xy}\right)$

$\sin (\arccos (x))=\sqrt{1-x^2}$

$\cos (\arcsin (x))=\sqrt{1-x^2}$

$\sin (\arctan (x))=\frac{x}{\sqrt{1+x^2}}$

$\cos (\arctan (x))=\frac{1}{\sqrt{1+x^2}}$

$\tan (\arcsin (x))=\frac{x}{\sqrt{1-x^2}}$

$\tan (\arccos (x))=\frac{\sqrt{1-x^2}}{x}$