A spectroscope is a device which measures the spectrum of light. Early spectroscopes were simply a prism with graduations marking wavelengths. Modern spectroscopes generally use a diffraction grating, a movable slit and some kind of photodetector[?], all automated and controlled by a computer.
... the left of "=", that will make it a perfect square trinomial of the form x2 + 2xy + y2. Since "2xy" in this case is (b/a)x, we must have y = b/(2a), so we add the square ...