Question: How to finding alpha(n) of this system equation(Help me!!!)

How to finding alpha(n) of this system equation finding alpha(n) whan n=1..3 cos(alpha(1))+cos(alpha(2))+cos(alpha(3))=3*pi/4; cos(5*alpha(1))+cos(5*alpha(2))+cos(5*alpha(3))=0; cos(7*alpha(1))+cos(7*alpha(2))+cos(7*alpha(3))=0; so.. i am basic maple user.herry herry.
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