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 .