Тригонометрия
\[ sin^2x+cos^2x=1 \] \[ cos^2x=1-sin^2x \] \[ cosx=\pm \sqrt{1-sin^2x} \] \[ sin^2x=1-cos^2x \] \[ sinx=\pm \sqrt{1-cos^2x} \] \[ tgx \cdot ctgx=1 \] \[ sin2 \alpha=2sin \alpha \cdot cos \alpha \] \[ cos2\alpha=cos^2\alpha – sin^2\alpha \] \[ cos2\alpha=1 -2 sin^2\alpha \] \[ cos2\alpha=2 cos^2\alpha – 1 \]