3. Let f(ax) be the function graphed below. -1 a) ESTIMATE the value of Jf() dax using a Riemann Sum with 4 equal subintervals. Let z be the left endpoint of each subinterval. Sketch the appropriate rectangles on the grid above. If instead of 4 rectangles, assume we use n rectangles. If xi is the right endpoint of the ith rectangle, write a representation for z b)