One of the roots of the equation 8x3 - 6x +1 = 0 is
a) cos 10o
b) cos 30o
c) sin 30o
d) cos 80o
Please reply with the solution.
Thank You
Using the formula,
cos 3x = 4cos3x - 3cos x
Putting x = 80°, we have
cos 240° = 4t3 - 3t
\(\Rightarrow -\frac{1}{2}=4t^3-3t\)
\(\Rightarrow 8t^3-6t+1=0\) which is same as the equation given. So, the equation satisfies x = 80°.
Options (b) and (c) can be checked by directly putting the values. Option (a) can be checked by using the method mentioned above.