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" For example, one time we were putting some numbers into a formula, and got to 48 squared. I reach for the Marchant calculator, and he says, “That’s 2,300.” I begin to push the buttons, and he says, “If you want it exactly, it’s 2,304.” The machine says 2,304. “Gee! That’s pretty remarkable!” I say. “Don’t you know how to square numbers near 50?” he says. “You square 50—that’s 2,500—and subtract 100 times the difference of your number from 50 (in this case it’s 2), so you have 2,300. If you want the correction, square the difference and add it on. That makes 2,304. "

― Steven H. Strogatz , The Joy of x: A Guided Tour of Math, from One to Infinity

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Steven H. Strogatz quote : For example, one time we were putting some numbers into a formula, and got to 48 squared. I reach for the Marchant calculator, and he says, “That’s 2,300.” I begin to push the buttons, and he says, “If you want it exactly, it’s 2,304.” The machine says 2,304. “Gee! That’s pretty remarkable!” I say. “Don’t you know how to square numbers near 50?” he says. “You square 50—that’s 2,500—and subtract 100 times the difference of your number from 50 (in this case it’s 2), so you have 2,300. If you want the correction, square the difference and add it on. That makes 2,304.
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