Question 57

The value of $$\sin 20^\circ \cos 70^\circ + \sin 70^\circ \cos 20^\circ$$ is:

Solution

$$\sin 20^\circ \cos 70^\circ + \sin 70^\circ \cos 20^\circ$$ = $$\sin20^{\circ}\cos70^{\circ}+\cos20^{\circ}\sin70^{\circ}$$

This is in the form of $$\sin A\cos B+\cos A\sin B=\sin\left(A+B\right)$$

$$=$$> $$\sin20^{\circ}\cos70^{\circ}+\sin70^{\circ}\cos20^{\circ}=\sin\left(20^{\circ\ }+70^{\circ}\right)= \sin90^{\circ\ }=1$$

Hence, the correct answer is Option A

Share on Whatsapp Share on Whatsapp

Create a FREE account and get: