an example in my text says that if the values for a, b and c are 2π, 2πh and -S respectively

with those values plugged into the quadratic equation you get

-2πh ± √πi^2 h^2 - 4(2π)(-S)

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4π

up to that point i follow what is going on but then the text reduces the formula to

-2πh ±2 √π^2 h^2 - 2πS

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4π

what I don't understand is how -4(2π)(-S) reduces to 2πS in the above equation.

from there we divide everything by 2 and get

-πh ± √πi^2 h^2 + 2πiS

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2π