The textbook for algebra and trigonometry for class XI published by the Punjab Text Book Board in Lahore uses these formulas often from Chapter 9 to Chapter 14. To help you recall the formulas, use this page. These formulas are all provided for trigonometric functions that have real values and are defined.

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### Three Steps to solve

Three Steps to solve

Step I: First check that is even or odd

Step II: If is even then the answer will be in and if the is odd then will be converted to and vice virsa (i.e. will be converted to ).

Step III: Now check in which quadrant is lying if it is in Ist or IInd quadrant the answer will be positive as is positive in these quadrants and if it in the IIIrd or IVth quadrant the answer will be negative.

e.g.

Since is odd so answer will be in and 667 is in IVth quadrant and is -ive in IVth quadrant therefore answer will be in negative. i.e

Similar technique is used for other trigonometric ratios. i.e and .