Question 1082992
{{{sin^2(x)+ cos^2(-x)= 2cos(pi/2-(x))}}}
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You're using more { } than necessary.
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cos(-x) = cos(x)
{{{sin^2(x)+ cos^2(x)= 2cos(pi/2-(x))}}}
{{{1 = 2cos(pi/2-(x))}}}
{{{cos(pi/2-(x)) = 1/2}}}

{{{sin(x) = 1/2}}}
x = pi/6, 5pi/6
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Write your answer as a multiple of pi if possible. 

When is that not possible?