Question

Ac²= 15²+15²-2*15*15*cos120
Вычислите

Answer 1

$AC^2 = 15^2 + 15^2 - 2\cdot 15 \cdot 15 \cdot \cos120^o = 225 + 225 - 450\cdot \left (-\dfrac{1}{2} \right ) = 450 - (-225) =\\\\= 450 + 225 = 675\\\\\\AC = \sqrt{AC^2} = \sqrt{675} = 15\sqrt{3}$