A complete turn has $360$ degrees, and each degree is divided into $60$ parts called minutes.

When the central angle with its vertex at the centre of the earth has a measure of $1$ minute, the arc on the surface of the earth that is formed by this angle (known as the great-circle distance) has a measure of $1$ nautical mile.

The radius of the earth is approximately $6371 \mathrm{km}$. Find how many $\mathrm{km}$ there are in $1$ nautical mile.

Find the sign of:

$\cos 130°$

Find the sign of:

$\sin 320°$

Find the sign of:

$\tan 225°$

Find an obtuse angle that has the same sine as:

$36°$       [Enter the value excluding degree symbol]

Find an obtuse angle that has the same sine as:

$50°$       [Enter the value excluding degree symbol]

Find an obtuse angle that has the same sine as:

$85°$       [Enter the value excluding degree symbol]

Find an obtuse angle that has the same sine as:

$460°$       [Enter the value excluding degree symbol]

Find an obtuse angle that has the same sine as:$\frac{\mathrm{\pi }}{3}$ is of the form of $\frac{m\mathrm{\pi }}{3}$, then $m=$