Question 207429
{{{Tan(x) (Cot(x) + Tan(x) ) = Sec^2x}}}
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Distribute to remove the parentheses:

{{{Tan(x)Cot(x) + Tan^2x  = Sec^2x}}}

Replace {{{Cot(x)}}} by {{{1/Tan(x)}}}

{{{ Tan(x) (1/Tan(x)) + Tan^2x  = Sec^2x}}}

{{{cross(Tan(x)) (1/cross(Tan(x))) + Tan^2x  = Sec^2x}}}

{{{1+Tan^2x= Sec^2x}}}

{{{Sec^2x=Sec^2x}}}

Edwin</pre>