Question 1034293
{{{(sec^2("12°")-1)tan^2(78)=1}}}
<pre>
Use a Pythagorean identity

{{{tan^2("12°")tan^2("78°")}}}

{{{tan^2("45°"-"33°")tan^2("45°"+"33°")}}}

Use double-angle formula:

{{{((tan("45°")-tan("33°"))/(1+tan("45°")tan("33°")))((tan("45°")+tan("33°"))/(1-tan("45°")tan("33°")))}}}

Use {{{tan("45°")=1}}}

{{{((1-tan("33°"))/(1+1*tan("33°")))((1+tan("33°"))/(1-1tan("33°")))}}}

{{{((1-tan("33°"))/(1+tan("33°")))((1+tan("33°"))/(1-tan("33°")))}}}

{{{(cross((1-tan("33°")))/(cross(1+tan("33°"))))((cross(1+tan("33°")))/(cross(1-tan("33°"))))}}}

{{{1}}}

Edwin</pre>