A number like 30 names a different angle in degree mode than in radian mode

Check the angle unit before evaluating

Open Graph Settings and choose Degrees or Radians to match the problem. Do not assume a fresh or previously used calculator has the unit you need.

In degree mode, $\sin(30)=1/2$. In radian mode, $\sin(\pi/6)=1/2$. Entering $30$ while the calculator interprets it as radians describes a different angle.

Choose sine, cosine, or tangent by the sides you know

Relative to an acute angle, sine is opposite over hypotenuse, cosine is adjacent over hypotenuse, and tangent is opposite over adjacent. If the hypotenuse is $18$ and the angle is $30^\circ$, the opposite side is $18\sin(30^\circ)=9$.

Draw or label the triangle before calculating. The hypotenuse is opposite the right angle, regardless of how the triangle is rotated. Also use $\sin(\theta)=\cos(90^\circ-\theta)$ for complementary acute angles.

$\displaystyle 18\operatorname{sin}\left(30\right)$

Opposite side, with the calculator in degree mode.

$\displaystyle \operatorname{arcsin}\left(\frac{3}{5}\right)$

An angle from a sine ratio, about 36.87 degrees in degree mode.

Inverse trig returns an angle

If an acute angle has sine $3/5$, use arcsin to find the angle. The output is approximately $36.87^\circ$ in degree mode. The unit choice affects the output of inverse trig as well as the input of ordinary trig.

A half turn is $180^\circ=\pi$ radians. Convert degrees to radians by multiplying by $\pi/180$, and radians to degrees by multiplying by $180/\pi$. For arc length $s=r\theta$, the angle $\theta$ must be in radians.

Keep practicing the connected skills