Question

What formula would I use to find A?

Answer 1

For this case by cosine theorem, we can use the following formula to find the value of a:
a ^ 2 = (6.3) ^ 2 + (15.10) ^ 2 - 2 * (6.3) * (15.10) cos (70)
Clearing a we have:
a = root ((6.3) ^ 2 + (15.10) ^ 2 - 2 * (6.3) * (15.10) cos (70))
Answer:
A formula to find A is:
a = root ((6.3) ^ 2 + (15.10) ^ 2 - 2 * (6.3) * (15.10) cos (70))