Question 1086707
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{{{sin(theta) - cos(theta)}}} = 0  ====>  {{{sin(theta)}}} = {{{cos(theta)}}}  ====>  (divide by {{{cos(theta)}}} both sides )  ====> 


{{{tan(theta)}}} = 1  ====>  {{{theta}}} = {{{pi/4}}}  or  {{{theta}}} = {{{5pi/4}}}.


So, EITHER {{{sin(theta)}}} = {{{cos(theta)}}} = {{{sqrt(2)/2}}}  OR

           {{{sin(theta)}}} = {{{cos(theta)}}} = {{{-sqrt(2)/2}}}.


In any case,  {{{sin^4(theta) + cos^4(theta)}}} = {{{1/4 + 1/4}}} = {{{2/4}}} = {{{1/2}}}.
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