Question

14sin35 * cos35 / sin70

Answer 1

sin2α=2sinα*cosα   Синус двойного угла.

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7*2*sin35 * cos35 / (2*sin35*cos35)=7.

70°=2*35°.

Answer 2

$\dfrac{14Sin35^\circ\cdot Cos35^\circ}{Sin70^\circ }=\dfrac{7\cdot2Sin35^\circ\cdot Cos35^\circ}{Sin70^\circ } =\dfrac{7\cdot Sin(2\cdot 35^\circ) }{Sin70^\circ }=\dfrac{7Sin70^\circ }{Sin70^\circ } =\boxed7$