I would advise
1. Stop arguing with the person who is trying to help you, instead do as you've been instructed so that you learn something and hopefully will be able to remember this for an exam.
2. Use the half-angle identities for sine, cosine and tangent to find the exact surd answers when your angle is . You can also find exact values when your angle is , or any successive half angle.
Oh so it's similar to using a special angle...
then use double angle formula to solve for x
Don't mind me asking but why is this type of question coming up when I don't learn anything about the special angles of tan15 and such? I have only heard of tan 30, tan 60, tan 90 and so on..
nowdays questions don't confine to only whatever you have learnt so be prepared . It's good that you learnt the extras . However , in this case , tan 15 is related to whatever you have learnt , the special angle and double angle formula .
Using the quadratic formula ,
is not possible because tan 15 is in the first quadrant , everything here will be positive .