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Question Number 119919 by bramlexs22 last updated on 28/Oct/20

$$\sin 70°\cos 50°+\sin 260°\cos 280°=?$$

Answered by bobhans last updated on 28/Oct/20

$$\iff \sin 70°\cos 50°+(-\cos 10°)\left(\sin 10°\right)=$$$$\frac{1}{2}(\sin 120°+\sin 20°)-\frac{1}{2}\sin 20°=$$$$\frac{1}{2}\times \frac{1}{2}\sqrt{3}=\frac{\sqrt{3}}{4}$$

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