Shankar
Last Activity: 5 Years ago
If 450°
So A is in the second quadrant.
so cos A = -√(1 - (336/625)²) = -527/625
I like tan(x/2) = (1 - cos(x))/sin(x) because it has no radicals in it.
tan(A/2) = (1 + 527/625)/(336/625) = 24/7
If 450°
A reference triangle for A/2 would then be y = -24, x = -7, r = 25
So cos(A/2) = -7/25 and sin(A/2) = -24/25
Then tan(A/4) = (1 - cos(A/2))/sin(A/2) = (1 + 7/25)/(-24/25) = -4/3
If 450°
A reference triangle for A/2 would then be y = 4, x = -3, r = 5
So sin(A/4) = 4/5
CHECK
We note that arcsin(336/625) = 0.5675882184 radians = 32.52040941662392°
which is in the first quadrant.
Subtract it from 180° and we get 147.47959058337608
which is in the second quadrant.
Add 360° and we get A = 507.4795905833761°
So sin(A/4) comes out 0.8 = 4/5