Sina = 3/5
Sina+COSA <; 0
As can be seen,
A & gt90 degrees
cosA = - 4/5
A^2 = b^2+c^2-200 BC
c^2 + b^2 - a^2 - 2bc cosA = 0
c^2 + 8c - 20 = 0
(c + 10)(c - 2) = 0
C 1 =- 10 (should be discarded)
c2 = 2
therefore
c = 2 .