Ideally how it should be set out:

define f(x)
    return x^2

define Algorithm()
    sum ← 0
    a ← 1
    b ← 2
    h ← 0.5
    left ← a
    right ← a + h

    while right ≤ b do
        arc ← sqrt(f(right) - f(left)^2 + h^2)
        sum ← sum + arc
        left ← left + h
        right ← right + h
    end while

    print sum



Alternatively and acceptably:

define f(x)
    return x^2

sum ← 0
a ← 1
b ← 2
h ← 0.5
left ← a
right ← a + h

while right ≤ b do
    arc ← sqrt(f(right) - f(left)^2 + h^2)
    sum ← sum + arc
    left ← left + h
    right ← right + h
end while

print sum