Solving for x given F(x) for nonlinear polynomial function

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Sara 2011-7-11

Hello my name is Sara I have a polynomial function that looks like this:

kp = {(1-b)^3/b^2}*{20/5-b}

I have the value for kp but I need to solve for b.

How can I do this in matlab.

Please help

Thank you

Walter Roberson 2011-7-11

b = roots([1, -7, 15-kp, -13, 4])

Walter Roberson 2011-7-12

kp = (1-b)^3/b^2*(4-b)

Multiply both sides by b^2 (assuming b is non-zero)

kp * b^2 = (1-b)^3*(4-b)

Expand the right hand side

kp * b^2 = 4-13*b+15*b^2-7*b^3+b^4

move the left side to the right to get

0 = 4-13*b+(-kp+15)*b^2-7*b^3+b^4

Reorder by descending powers of b, take the coefficients and write the roots() expression.

bym 2011-7-13

doh! :(

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