solution for 1st case:
Given:(x1,y1),(x2,y2),(x3,y3),the co-ordinates of the
vertices of the triangle.
 Let (xx,yy) be the pt to be located.
 Find the equations of the lines {(x1,y1),(x2,y2)} and
{(x1,y1)(x3,y3)} using the formula 
((y-y1)/(y2-y1))=((x-x1)/(x2-x1))

 Now substitute the y value  in the 2 equations got. You 'll
be getting the x limits. If the given x value lies within
the limits you have found,the given pt is within the
triangle or else it is not.