Question 395311
understand that csc(a)=1/sin(a)
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work with the left hand of the equation to get the right hand side
{{{cos^2(a)/csc^2(a)+cos^4(a)}}}
= {{{cos^2(a)/(1/sin^2(a))+cos^2(a)}}}  substitute csc(a)=1/sin(a)
={{{cos^2(a)*sin^2(a)+cos^4(a)}}}  invert
={{{cos^2(a)*(sin^2(a)+cos^2(a))}}}   factor out a cos^2(a)
={{{cos^2(a)*1}}}   indetity {{{sin^2(a)+cos^2(a)=1}}}