Product To Sum Cos·Cos And Sin·Sin identity (2cos Acos B=cos(A-B)+cos(A+B); 2sin Asin B=cos(A-B)-cos(A+B))
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2cos Acos B=cos(A-B)+cos(A+B); 2sin Asin B=cos(A-B)-cos(A+B)
What each symbol means
| Symbol | What it stands for |
|---|---|
| A, B, x, a, b | As in standard NCERT treatment; domain restrictions apply for tan. |
When to use this
Standard NCERT conditions; tan identities exclude odd multiples of π/2 where undefined.