Asked by Fred
2x^3 + x^2 - 5= 0
x=?
Is this possible to solve?
x=?
Is this possible to solve?
Answers
Answered by
Lizzie
Yea. x=1.209355. You have to find the roots.
Answered by
Fred
Thank you, but how you made that? What was the process?
Answered by
Reiny
There is no "nice" formula for solving cubics.
We can graph y = 2x^3 + x^2 - 5 and get an approximate answer form the graph
http://www.wolframalpha.com/input/?i=plot+y+%3D+2x%5E3+%2B+x%5E2+-+5
and "guess" at appr 1.2
You can nibble away at the answer using a calculator
x = 1, y = 2+1-5 = -2 , too low
x = 1.2 , y = -.0104 , a bit too low but close
x = 1.21, y = .00722 , a bit too high but very close
x = 1.205 , y = -.048 , a bit too low but close
so x is between 1.205 and 1.21
you get the idea ?
If you know Calculus, use Newton's method.
let me know if you study Calculus before I show you that method
We can graph y = 2x^3 + x^2 - 5 and get an approximate answer form the graph
http://www.wolframalpha.com/input/?i=plot+y+%3D+2x%5E3+%2B+x%5E2+-+5
and "guess" at appr 1.2
You can nibble away at the answer using a calculator
x = 1, y = 2+1-5 = -2 , too low
x = 1.2 , y = -.0104 , a bit too low but close
x = 1.21, y = .00722 , a bit too high but very close
x = 1.205 , y = -.048 , a bit too low but close
so x is between 1.205 and 1.21
you get the idea ?
If you know Calculus, use Newton's method.
let me know if you study Calculus before I show you that method
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