Question

f(x)=x√
let the area under the graph f(x) over the interval [0,1] be A. Prove that
.51leA≤.77
by computing R4, and L4. Explain your reasoning.

Here is what I am getting for R4-
f(x)=x√

Δx=1−04→1/4

after putting things together I am left with
∑01j14−−−√
but it evaluates out to .5 and does not fit into the proof.
Ideas?