Question #f85e4

1 Answer
Feb 25, 2018

The Soln. Set #={k/5+-1/20, k in ZZ}#.

Explanation:

Recall that, #costheta=cosalpha rArr theta=2kpi+-alpha, k in ZZ.#

#:. cos(10pix)=0=cos(pi/2) rArr 10pix=2kpi+-pi/2, k in ZZ#.

#rArr x=(2kpi+-pi/2)/(10pi)=(2kpi)/(10pi)+-(pi/2)/(10pi), k in ZZ#.

# rArr x=k/5+-1/20, k in ZZ#, giving us,

The Soln. Set #={k/5+-1/20, k in ZZ}#.