Question

The cosine of 48°, to the nearest hundredth, is 0.67. To the nearest hundredeth, what is the cosine of 96°? How do find this out with out a calculator?

Answer 1

96 = 2*48
use formulae for cos(2x)

Answer 2

yeah use the formula for cos(2x)
\[ \cos 2x=2\cos ^{2}x-1\]
x=48
this gives the value approx. to '-0.1391'