Estimate the square root between two consecutive whole numbers of sqrt [55]

9514 1404 393

  7.4 . . . . between 7 and 8

Step-by-step explanation:

55 is between the perfect squares 49 = 7² and 64 = 8². Using linear interpolation, the square root is approximately 7 +(55-49)/(64-49) = 7 6/15 = 7.4

√55 ≈ 7.4 . . . . approximate root by linear interpolation

Additional comment

A way to improve the estimate of the root is to use the "Babylonian method" of iterating the root. Divide the original number (55) by the estimate of the root, and average that result with the estimate:

  next best guess = (55/7.4 +7.4)/2 = 7 77/185 ≈ 7.4162_162(repeating)

This matches the actual root when rounded to 4 decimal places. The number of accurate decimal places approximately doubles with each iteration.

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Another way to improve the estimate is to modify the fractional portion. (The above method converges on a root more quickly.) For this, the iteration of the fractional part of the root is ...

  next fractional part = 6/(14 +(fractional part))

where 6/14 is the linear estimate fractional value with 1 subtracted from its denominator.

For one iteration, the new estimate of the fractional part is 6/(14 +6/15) = 5/12, so the root estimate is about 7.4167 compared to the above 7.4162.

linear pair postulates