we know that
tan 2A = 2tanA/(1 - tan^2 A)
so tan 210 = 2tan105/(1 - tan^2 105)
you should know that
tan 210 = tan 30° = 1/√3
let tan 105 = x
1/√3 = 2x/(1-x^2)
2√3x = 1 - x^2
x^2 + 2√3 - 1 = 0
x = (-2√3 ± √16)/2
= -√3 ± 2
but obviously tan105 is negative, ( 105° is in II )
so tan 105° = -√3-2
Trig - find cos x/2, sin x = 1/4, 360 < x < 450, use half-angle identity
Trigonometry - use the appropriate trig identity (sum and difference, half angle...
Trig - Use a half-angle identity to find the exact value for sec(x/2) if sinx...
Trig - Find the exact value of tan 5pi/12 using the half-angle identity.
trig - Find the exact value by using a half-angle identity. cos 22.5 degrees
trig - find the exact value by using the appropriate half-angle identity: sin(...
trig - A coil of wire rotating in a magnetic field induces a coltage E=20sin((...
trig - using the fact that 5pi/8=1/2(5pi/8) and the half angle identity for cos ...
trig - Use the half angle formula to find cos(pi/12)
Math - Use a double or half angle identity to find the exact value of the ...