bismillah, tolong bantuin dong no 9-16, aku kasih poin banyak deh, biar nanti jawabannya aku pahamin

10.
a^2 = b^2 + c^2 - 2×b×c×cos A
a^2 = 8^2 + 5^2 - 2×8×5×1/2
a^2 = 64 + 25 - 40
a^2 = 49
a = 7
no 15.. masih ragu
tan a = akar 3/3
= 1/ akar3(b)