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a)
kuusikulmion kulmien summa on
\left(6-2\right)\cdot180°=720°
\frac{720°}{6}=120°
b)
\frac{\left(n-2\right)\cdot180°}{n}
\frac{180°n-360°}{n}\ \parallel\cdot n
180°-\frac{360°}{n}