[tex]\cot\left(\dfrac\pi2-\theta\right)=\dfrac{\cos\left(\dfrac\pi2-\theta\right)}{\sin\left(\dfrac\pi2-\theta\right)}=\dfrac{\cos\dfrac\pi2\cos\theta+\sin\dfrac\pi2\sin\theta}{\sin\dfrac\pi2\cos\theta-\cos\dfrac\pi2\sin\theta}=\dfrac{\sin\theta}{\cos\theta}=\tan\theta[/tex]
