Question

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Numărul sin190+sin10 este egal cu?
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Answer 1

$\displaystyle\bf\\\boxed{\bf de~retinut:~sinx+siny=2sin\frac{x+y}{2}cos\frac{x-y}{2}}~.\\\\---------------------------------\\\\sin(190^{\circ})+sin(10^{\circ})=2sin\frac{190^{\circ}+10^{\circ}}{2}cos\frac{190^{\circ}-10^{\circ}}{2} =2sin(100^{\circ})\cdot cos(90^{\circ})=0.\\\\\boxed{\bf cos(90^{\circ})=0}~.$