Solving the equation:
x3-300x=2961 was one of the problems in Oxford entrance requirements.
A solution published on the web is based on calculus which was not to be assumed as possessed by all applicants.
I ‘ve solved it p&p, and almost in no time.
Request to provide a KISS (sans calculus) solution.
Only numbers that end in 1 have a last digit 1.
20^3 - 300*20 = 8000 - 6000 = 2000 so a solution must be just a little larger. It must be 21.
21^3 - 200*31 = 9261 - 6200 = 2961
To find the other solutions, use synthetic division to factor (x-21) out of x^3 - 300x - 2961
which gives x^2+21x+141
the remaining solutions can easily be found with the quadratic formula. The discriminant is -123 so they are complex conjugates.
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Posted by Jer
on 2022-12-13 11:08:51 |
My way
