Sum To Product Cos±Cos identity (cos A+cos B=2cosfracA+B2cosfracA-B2; cos A-cos)
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cos A+cos B=2cosfracA+B2cosfracA-B2; cos A-cos B=-2sinfracA+B2sinfracA-B2
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.