Answer:
BC = 88.88
Explanation:
Comment.
This looks like an example of the cos law.
Givens
AB = 100 m
<A = 60 degrees
AC = 70 m
Cos(60) = 1/2
BC = ?
Formula
BC^2 = AB^2 + AC^2 - 2*AB*AC * Cos(60)
Solution
BC^2 = 100^2 + 70^2 - 2*100*70 * 1/2 1/2 and 2 cancel out
BC^2 = 10000 + 4900 - 7000
BC^2 = 7900 Take the sqr root of both sides
√BC^2 = √7900
BC = 88.88