For the triangle question. Use cosine rule to find an angle between any of the two sides, and then use the formula (1/2)absin(theta) for the area.
for instance. let the sides be a, b and c. the angle between a and b is given by:
c^2 = a^2 + b^2 - 2abcos(C), where C is the angle between a and b. Solve for C.
then, use the formula A = (1/2)absin(C) to find the area