Finding the exact value of sin(18 degrees)

This is one classic way to find the exact value of sin(18 degrees), i.e sin(pi/10). We will use the double angle identity for sin(2x), the triple angle identity for cos(3x) (proof here 👉    • cos(3x) in terms of cos(x)  ), and the quadratic formula! I love this so much because this covers so much! Enjoy! sin(18 degrees) by using a special right triangle:    • this special triangle gives us sin(18º)   ---------------------------------------- 💪 Support this channel and get my math notes by becoming a patron:   / blackpenredpen   🛍 Shop my math t-shirt & hoodies: https://amzn.to/3qBeuw6 ----------------------------------------