Evaluate the following:

$\sin 690°\cos 930°+\tan \left(-765°\right)cosec\left(-1170°\right)$

Evaluate the following:

${\sin }^2\frac{\pi }{8}+{\sin }^2\frac{3\pi }{8}+{\sin }^2\frac{5\pi }{8}+{\sin }^2\frac{7\pi }{8}$

Evaluate the following:

${\sin }^2\frac{\pi }{4}+{\sin }^2\frac{3\pi }{4}+{\sin }^2\frac{5\pi }{4}+{\sin }^2\frac{7\pi }{4}$

Evaluate the following:

$\tan \frac{\pi }{12}\tan \frac{\pi }{16}\tan \frac{5\pi }{12}\tan \frac{7\pi }{16}$

$\frac{\cos x}{\sin \left(\frac{\pi }{2}+x\right)}+\frac{\sin (-x)}{\sin (\pi +x)}-\frac{\tan \left(\frac{\pi }{2}+x\right)}{\cot x}=$

$\frac{\sin (\pi +x)\cos \left(\frac{\pi }{2}+x\right)\tan \left(\frac{3\pi }{2}-x\right)\cot (2\pi -x)}{\sin (2\pi -x)\cos (2\pi +x)cosec(-x)\sin \left(\frac{3\pi }{2}+x\right)}=$

Find $y$ from the following equation:

$cosec\left(\frac{\pi }{2}+x\right)+y\cos x\cot \left(\frac{\pi }{2}+x\right)=\sin \left(\frac{\pi }{2}+x\right)$