how can i find x value from given y (6th degree polynomial)
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firrou bouteflika
on 9 Jul 2021
Commented: firrou bouteflika
on 19 Dec 2021
y = [7 12 18 27 35 39];
p1 = 3.7739e-21
p2 = -6.5969e-17
p3 = 2.2715e-13
p4 = 1.1034e-09
p5 = -4.8986e-06
p6 = 0.010416
p7 = -0.70896
y = p1*x^6 + p2*x^5+p3*x^4+p4*x^3+p5*x^2+p6*x+p7;
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Accepted Answer
Matt J
on 9 Jul 2021
x=roots([p1,p2,p3,p4,p5,p6,p7-y])
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Walter Roberson
on 19 Dec 2021
format long g
p = [3.7769e-21, -6.6055e-17, 2.2806e-13, 1.0989e-09, -4.8887e-06, 0.010408, -0.71229];
R = roots(p)
realroots = R(imag(R)==0)
syms x
poly = poly2sym(p)
fplot([poly,0], [-4750 250])
It is a degree 6 polynomial in real coefficients. There are always going to be an even number of real roots: in this case there are two real roots. You can never get just one real root for a polynomial of even order that has real coefficients.
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