Is there a formula for the height in left hand sums? I know that for right hand it's f(x_i), being ''
x_i= a+([b-a]/n)*i'' in [a,b].
I'd like to know how to calculate x_i in left hand sums. I'd also like to know what does x_i+1 and x_i-1 stand for? Thank you very much, i hope you can help me