Question #142403
Use Mu ̈ller’s method to determine the real and complex roots of
f (x) = x^4 − 2x^3 + 6x^2 − 2x + 5
1
Expert's answer
2020-11-05T13:56:49-0500

Let f(x)=x42x3+6x22x+5f(x)=x^4-2x^3+6x^2-2x+5

Use initial guesses x0=1,x1=0,x2=1x_0=-1, x_1=0, x_2=1

f(x0)=f(1)=16f(x_0)=f(-1)=16

f(x1)=f(0)=5f(x_1)=f(0)=5

f(x2)=f(1)=8f(x_2)=f(1)=8

h0=x1x0=0(1)=1h_0=x_1-x_0=0-(-1)=1

h1=x2x1=10=1h_1=x_2-x_1=1-0=1

δ0=f(x1)f(x0)h0=5161=11\delta_0=\dfrac{f(x_1)-f(x_0)}{h_0}=\dfrac{5-16}{1}=-11

δ1=f(x2)f(x1)h1=851=3\delta_1=\dfrac{f(x_2)-f(x_1)}{h_1}=\dfrac{8-5}{1}=3

a=δ1δ0h1+h0=3(11)1+1=7a=\dfrac{\delta_1-\delta_0}{h_1+h_0}=\dfrac{3-(-11)}{1+1}=7

b=a×h1+δ1=7×1+3=10b=a\times h_1+\delta_1=7\times1+3=10

c=f(x2)=f(1)=8c=f(x_2)=f(1)=8

x3=x2+2cb±b24acx_3=x_2+\dfrac{-2c}{b\pm\sqrt{b^2-4ac}}

x3=1+2(8)10+1024(7)(8)=x_3=1+\dfrac{-2(8)}{10+\sqrt{10^2-4(7)(8)}}==0.285714+0.795395i=0.285714+0.795395i

x0=1,x1=0,x2=0.285714+0.795395ix_0=-1, x_1=0, x_2=0.285714+0.795395i

Calling the function Muller with different parameters yields two complex roots of the equation x1i,x31+2i.x_1\approx i, x_3\approx1+2i. Two other roots can be determined as their conjugate pairs x2i,x412i.x_2\approx-i, x_4\approx1-2i.


x1ix_1\approx i

x2ix_2\approx -i


x31+2ix_3\approx 1+2i

x412ix_4\approx 1-2i


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