How do I do:

Show that for all x E (0, pi), the area of a triangle with side lengths a and b and with included angle x is A= 1/2(a)(b)(sin x) (Hint: You need to consider two cases.)

and

2sin^2 x - 5sin x + 3 < 0 in interval [0, 2pi)

Can someone help me a bit please :P

Thanks!