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WindUponWaves's avatar

I managed to solve the math question the grinding way (get out a piece of paper, expand everything, add and subtract all the terms from each other, get a result, pick the leading order term), then remembered that you can just use the approximation (1 + a) / (1 + b) = a/b for a and b much less than 1. There's some other terms as well of course, but we'll throw them out in the end, so approximating to the leading term during the calculation isn't a truncation error. With that approximation, the question simplifies to "-10^[-4] + 3*10^[-4]", which is just 2*10^(-4), which is D. So there's the answer: just get an intuition that only the leading term matters when dealing with an expression that uses the likes of 10^(-4) vs. 10^(-8).

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Doug Mounce's avatar

This is suggested under the second principle, Devise a Plan, in Polya's classical heuristic, How to Solve It.

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