Welcoming you in another post of the series “Trigonometry”. We shall discuss four very important formulas of Trigonometry which is widely known as “C-D Formula”.
\(\sin{\text{C}}+\sin{\text{D}}=2\sin(\frac{\text{C}+\text{D}}{2})\cos(\frac{\text{C}-\text{D}}{2})\)
\(\sin{\text{C}}-\sin{\text{D}}=2\cos(\frac{\text{C}+\text{D}}{2})\sin(\frac{\text{C}-\text{D}}{2})\)
\(\cos{\text{C}}+\cos{\text{D}}=2\cos(\frac{\text{C}+\text{D}}{2})\cos(\frac{\text{C}-\text{D}}{2})\)
\(\cos{\text{C}}-\cos{\text{D}}=-2\sin(\frac{\text{C}+\text{D}}{2})\sin(\frac{\text{C}-\text{D}}{2})\)
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