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Published byLynn Anthony Modified over 9 years ago
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Do this (without a calculator!) 42.5 x 37.6
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A blast from the past Slide Rules
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Logarithms were invented by the Scottish mathematician and theologian John Napier and first published in 1614. He was looking for a way of quickly solving multiplication and division problems using the much faster methods of addition and subtraction. Napier's way of doing this was to invent a group of "artificial" numbers as a direct substitute for real ones.
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He called this numbering system logarithms (which is Greek for "ratio-number", apparently). Logarithms are consistent, related values which substitute for real numbers. Incidentally, it wasn't until a few years later, in 1617, that a fellow mathematician named Henry Briggs adapted Napier's original "natural" logs to the more commonly used and convenient base 10 format.
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To see how these are useful for multiplication, consider what happens if you want to multiply 10 x 1,000, as a simple example. The secret here is that you could just add their logs together and then take the anti-log of the result. Why? Because log xy = Source: http://www.sliderule.ca/intro.htmhttp://www.sliderule.ca/intro.htm
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How do logs help in multiplication? 2 x 3 = y Log (2 x 3) = log y Log 2 + log 3 = log y.301 +.477 = log y.778 = log y 10.778 = y y = 6
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To find log x: 1. Line up cursor with x on D scale 2. Read number on L scale 3. Add “1” to your answer for each number past the ones place Ex. Find log 25 Line up cursor with 2.5 on D scale Read number on L scale Because there’s a number in the 10’s spot, add 1.
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Use the slide rule to find the following logs. 1. Log 3 2. Log 8 3. Log 1.2 4. Log 38 5. Log 52 6. Log 135
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What number has a log of... 1. 0.6 2. 1.37 3. 2.2
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To multiply (xy): 1. Line up "1" of C scale with x on D scale 2. Set hairline of cursor over y on C scale. 3. Answer is number on D scale Ex. Multiply 2x3: Line up "1" on C scale with 2 on D-scale Move cursor to 3 on C scale Read # on D scale
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Do these: 1. 15 x 4 2. 18 x 3.7 3. 1.5 x 2.3 4. 280 x 0.34 5..0215 x 3.54
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To divide ( x ÷ y ): 1. Line up x on D scale with y on C scale. 2. Answer lines up with “1” on D scale. Ex. Divide 8 ÷ 4 1. Line up 8 on D scale with 4 on C scale 2. Move cursor to 1 on C scale 3. Read # on D scale
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Do these: 1. 15 ÷ 3 2. 62.4 ÷.707 3. 23 ÷ 1.6 4. 0.53 ÷ 7
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Combining Operations 1. Think of problem as 2. Line up x on D scale with z on C scale 3. Move cursor to y on C scale 4. Read answer on D scale
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Do these: 1. 2. 3. 4.
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