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Saturday, February 20, 2021

2021/010) Simplify \cot 70^\circ +4\cos70^\circ=

 \cot 70^\circ +4\cos70^\circ=

=\frac{\cos 70^\circ}{\sin 70^\circ} +4\cos70^\circ=

=\frac{\cos 70^\circ + 4\sin 70^\circ \cos 70^\circ}{\sin 70^\circ }

=\frac{\cos 70^\circ +2(2\sin 70^\circ \cos 70^\circ)}{\sin 70^\circ }

=\frac{\cos 70^\circ +2\sin 140^\circ}{\sin 70^\circ }

=\frac{\sin 20^\circ +2\sin 40^\circ}{\sin 70^\circ }

=\frac{(\sin 20^\circ +\sin 40^\circ) + \sin 40^\circ}{\sin 70^\circ }

=\frac{(2 \sin 30^\circ \cos 10^\circ) + \sin 40^\circ}{\sin 70^\circ } using sin A + sin B formula

=\frac{\cos 10^\circ  + \sin 40^\circ}{\sin 70^\circ } 

=\frac{\sin 80^\circ + \sin 40^\circ}{\sin 70^\circ } 

=\frac{2  * \sin 60^\circ  \cos 20^\circ}{\sin 70^\circ } 

=\frac{\sqrt{3} \sin 70^\circ}{\sin 70^\circ }

=\sqrt{3}


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