Question 695869
The cosine function has period {{{ 360^0 }}}
So {{{ cos(x+n*360^0 ) = cos(x) }}}
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So we can write as follows:
{{{ cos( -1380 ) = cos( -300 + 1080 ) = cos( -300 + 4*360 ) = cos( -300 ) = 0.5 }}}