Question

use a formula sheet (i never got it) to help answer this:

sin(75degrees)

Answer 1

I suspect you need the sine of the sum of two angles, 45+30

Sin(A+B)=SinAcosB+cosAsinB

http://www.sosmath.com/trig/Trig5/trig5/trig5.html

I suspect you are suffering from lack of routine use of flash cards. Millions of students before you have suffered through memorizing these, as I did 55 years ago. Surely you can bear the pain.

Answer 2

I will make a guess at what is intended:

75 = 90 - 15
sin (a-b) = sin a cos b - cos a sin b
so
sin 90 cos 15 - cos 90 sin 15
= 1 cos 15 - 0 sin 15
= cos 15

15 = 30/2
cos a/2 = sqrt [(1+cos a)/2]
so
sqrt [ (1 + cos 30)/2 ]
but cos 30 = sqrt 3/2
so
sqrt [ (2+sqrt 3)/4 ]