9514 1404 393
Answer:
multiply by (d/cos(36°))
Step-by-step explanation:
As with any division problem, the equation remains true if you swap the divisor and the quotient (short answer).
cos(36°) = 16/d
d = 16/cos(36°) = 16/0.8090169943749475 ≈ 19.77708763999635
d ≈ 19.78
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Here is the longer answer, with respects to the properties of equality. The multiplication and division properties of equality tell you equality only holds if the same operation is performed to both sides of the equal sign. So, when we say "multiply by __", we mean that operation to be performed on boths sides of the equation.
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The two operations, <em>multiply by d</em> and <em>divide by cos(36°)</em> can be combined into one: <em>multiply by d/cos(36°)</em>. Once you realize this has the effect of the quotient (cos(36°)) and the divisor (d) trading places, you realize you don't need to take 3 steps to do what you can do in 1 step.
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<em>Comment on numerical precision</em>
We have kept the 16-digit precision of the numbers shown in the question, "just because." The final answer has 4 significant digits, so there is no real need to keep more than about 6 significant digits.