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# FP1 Linear Interpolation Ex2B Watch

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1. Hi!

I'm trying to complete this question from the FP1 textbook:

Find an approximation to the root of x3 - 3x - 5 = 0 using linear interpolation to 1.d.p given that the root lies between 2 and 3.

I keep getting 2.1875 as my first approximation, but the book and solution bank suggests otherwise. I have looked on other discussions and everyobe says that the solution bank is wrong but when I plotted the graph the solutionbanks answer is correct. Does this mean that there is a secret forumla that I don't know about.

Solution bank:

My answer:

The solution bank has switched the 13 and 3 around on the fraction but this seems to work only on questions when the gradient of the line is getting steeper instead of more sloped.

Thanks!
2. BUMBBBBBBB, i really need help!

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Updated: October 8, 2016
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