Wrong move:

Using SOHCAHTOA ratios for non-right-angled triangles without splitting them or using the sine/cosine rules first.

Why:

SOHCAHTOA only applies to triangles with a 90° angle, so using it for other triangle types produces invalid results.

Correct move:

Use the sine or cosine rule for any triangle without a right angle, or split the triangle into two right-angled segments if appropriate.

Wrong move:

Forgetting that sine is positive in both the first and second quadrants when solving trigonometric equations, leading to missing valid solutions.

Why:

The sine function is symmetric across 90°, so it returns the same value for θ and 180°-θ in the 0° to 360° range.

Correct move:

Always check for both valid solutions in the given angle range when solving equations involving the sine function.

Wrong move:

Mixing up side and angle pairings when applying the sine or cosine rule.

Why:

Both rules rely on matching each side to the angle directly opposite it, so misaligned labels lead to calculation errors.

Correct move:

Label triangles with side $a$ opposite angle $A$, side $b$ opposite angle $B$, etc. before applying either rule.