Hi, Could someone please help me prove this identity? sinA + sin9A = 2.sin5A.cos4A Thanks, your help would be very much appreciated!
Follow Math Help Forum on Facebook and Google+
Originally Posted by sammysparrow Hi, Could someone please help me prove this identity? sinA + sin9A = 2.sin5A.cos4A Thanks, your help would be very much appreciated! Use the trigonometric identity $\displaystyle \displaystyle\ SinA+SinB=2Sin\left(\frac{A+B}{2}\right)Cos\left(\ frac{A-B}{2}\right)$ with $\displaystyle B=9A$ coupled with $\displaystyle Cos(-C)=CosC$
Thanks Archie Meade!
View Tag Cloud