Question 359677
Let {{{C=cos(x)}}}, {{{S=sin(x)}}}, {{{T=tan(x)=S/C}}}

{{{ (C^2*S^2)/(T^2*(1-S^2))= (C^2*S^2)/(T^2*C^2)}}}
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{{{ (C^2*S^2)/(T^2*(1-S^2))= (S^2)/(T^2)}}}
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{{{ (C^2*S^2)/(T^2*(1-S^2))= (S^2)/(S^2/C^2)}}}
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{{{ (C^2*S^2)/(T^2*(1-S^2))= C^2}}}
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{{{ (C^2*S^2)/(T^2*(1-S^2))= highlight((cos(x))^2)}}}