The original worked lessons remain the main explanations. Use these focused reminders to check the conditions before you start.
Trigonometric equations on a stated interval
Find every solution in a finite interval.
Transform both interval endpoints for a multiple or shifted argument.
Handle degrees, radians, principal values and open endpoints consistently.
Work on the full argument interval before converting back to \(x\). Use every relevant sine/cosine branch and the tangent period. Check included endpoints, rejected endpoints and the original expression. A single inverse-calculator value is rarely the complete answer.