## Trigonometry (11th Edition) Clone

$\csc$ needs to be filled in the blank.
$$\cos70^\circ=\frac{1}{A20^\circ}\hspace{1cm}(1)$$ From the Cofunction Identity: $$\cos\theta=\sin(90^\circ-\theta)$$ So $$\cos70^\circ=\sin(90^\circ-70^\circ)=\sin20^\circ$$ Also, from Reciprocal Identity: $$\sin\theta=\frac{1}{\csc\theta}$$ Therefore, $$\cos70^\circ=\frac{1}{\csc20^\circ}$$ We thus need to fill in the blank with $\csc$.