TO WHILE away the last few days waiting for the new Harry Potter book, try your hand at this. The bell-shaped curve above is obtained by solving the equation y(a2 + x2) = a3. It is applied by physicists today to describe the distribution of the energy from stars at different X-ray and optical wavelengths, for example, and also the power dissipated in resonant circuits. The curve got its name from an 18th-century mathematician called Maria Gaetana Agnesi. But this doesn’t help us solve the greatest mystery about the curve: why is it called the Witch of…
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