Let \theta be an acute angle. If $\cos \theta = \frac{1}{4},$ then what is $\sin \theta?$
I found this on socratic
https://socratic.org/questions/sin-theta-1-4-what-is-the-value-of-costheta#452775 - you should find the answer there
hope that helps!
sin (theta) = sqrt [ 4^2 - 1^2] / 4 = sqrt (15) / 4