Calculati sin 100 + cos 100 - a, stiind ca sin 80 - cos 80 = a.
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[tex]\it sinx=sin(180^o-x);\ \ \ \ \ cosx=-cos(180^o-x)\\ \\ Pentru\ a=sin80^o-cos80^o, expresia\ devine:\\ \\ (sin100^o-sin80^o)+(cos100^o+cos80^o)=0+0=0[/tex]