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First Semester in Numerical Analysis with Julia, 2020a

First Semester in Numerical Analysis with Julia, 2020a

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CHAPTER 2. SOLUTIONS OF EQUATIONS: ROOT-FINDING 52<br />

A quantity and its 1/4 added together become 15. What is the quantity?<br />

Assume 4.<br />

\1 4<br />

\1/4 1<br />

Total 5<br />

As many times as 5 must be multiplied to give 15, so many times 4 must be<br />

multiplied to give the required number. Multiply 5 so as to get 15.<br />

\1 5<br />

\2 10<br />

Total 3<br />

Multiply 3 by 4.<br />

1 3<br />

2 6<br />

\4 12<br />

The quantity is<br />

12<br />

1/4 3<br />

Total 15<br />

Arya’s <strong>in</strong>structor knows she has taken math classes and asks her if she could decipher<br />

this solution. Although Arya’s <strong>in</strong>itial reaction to this assignment can be best described<br />

us<strong>in</strong>g the word "despair", she quickly realizes it is not as bad as she thought. Here is<br />

her thought process: the question, <strong>in</strong> our modern notation is, f<strong>in</strong>d x if x + x/4 =15.<br />

The solution starts <strong>with</strong> an <strong>in</strong>itial guess p =4. It then evaluates x + x/4 when x = p,<br />

and f<strong>in</strong>ds the result to be 5: however, what we need is 15, not 5, and if we multiply both<br />

sides of p + p/4 =5by 3, we get (3p)+(3p)/4 =15. Therefore, the solution is 3p =12.

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