Answer:
BC = 14.317821
Explanation:
Carnot’s theorem
BC^2 = AB^2 + AC^2 - 2 * AB * AC * cos(BAC)
BC^2 = 10^2 + 5^2 - 2 * 10 * 5 * -4/5
BC^2 = 100 + 25 -20 * -4
BC^2 = 125 + 80
BC^2 = 205
BC = √205
BC = 14.317821 cm
We use negative value of cos because we know that BC is the the longest side: in the operation we have - * - = +