Question 895850
Why we should solve like this?

If {{{CosX = -1/2}}}

{{{CosX = Cos(2(pi))/3}}}

{{{X = 2n(pi) +- 2(pi)/3}}}

Why can't we solve like this???

{{{CosX = -1/2}}}

{{{CosX = -Cos(pi)/3}}}
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cos(-x) <> -cos(x)
cos(-x) = cos(x)
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{{{CosX = Cos(-(pi))/3}}}

Because we can put minus sign inside in Cos...

{{{X = 2n(pi) +- (-pi)/3}}}