Question #305567

The fourth-degree polynomial

f(x) = 230x4 + 18x3 + 9x2 - 221x - 9

has two real zeros, one in [-1; 0] and the other in [0; 1]. Attempt to approximate these zeros to within

10-2 using the

(a)

Secant method(Use the endpoints of each interval as the initial approximations),

(b)

Newtons method(Use the midpoints of each interval as the initial approximation)


1
Expert's answer
2022-03-07T07:01:02-0500

f(x)=230x4+18x3+9x2221x9[1,0],[0,1]f(x)=230x^4+18x^3+9x^2-221x-9\\ \left[-1,0\right] , \left[0,1\right]

a)

a0=1,b0=0f(a0)=f(1)=23018+9+2219=433f(b0)=f(0)=9p2=a0b0a0f(b0)f(a0)f(a0)==10+19433433=0.0204a1=0.0204,b1=0f(a1)=f(0.0204)==230(0.0204)4+18(0.0204)3++9(0.0204)2221(0.0204)9=4.488f(b1)=f(0)=9p3=a1b1a1f(b1)f(a1)f(a1)==0.02040+0.02049+4.488(4.488)=0.0408p3p2=0.0204a2=0.0408,b2=0f(a2)=f(0.0408)==230(0.0408)4+18(0.0408)3++9(0.0408)2221(0.0408)9=0.034f(b2)=f(0)=9p4=a2b2a2f(b2)f(a2)f(a2)==0.04080+0.040890.034(0.034)=0.0408p4p3=0x=0.0408a_0=-1, b_0=0\\ f(a_0)=f(-1)=230-18+9+221-9=433\\ f(b_0)=f(0)=-9\\ p_2=a_0-\frac{b_0-a_0}{f(b_0)-f(a_0)}f(a_0)=\\ =-1-\frac{0+1}{-9-433}\cdot433=-0.0204\\ a_1=-0.0204, b_1=0\\ f(a_1)=f(-0.0204)=\\ =230(-0.0204)^4+18(-0.0204)^3+\\ +9(-0.0204)^2-221(-0.0204)-9=-4.488\\ f(b_1)=f(0)=-9\\ p_3=a_1-\frac{b_1-a_1}{f(b_1)-f(a_1)}f(a_1)=\\ =-0.0204-\frac{0+0.0204}{-9+4.488}\cdot(-4.488)=-0.0408\\ |p_3-p_2|=0.0204\\ a_2=-0.0408, b_2=0\\ f(a_2)=f(-0.0408)=\\ =230(-0.0408)^4+18(-0.0408)^3+\\ +9(-0.0408)^2-221(-0.0408)-9=0.034\\ f(b_2)=f(0)=-9\\ p_4=a_2-\frac{b_2-a_2}{f(b_2)-f(a_2)}f(a_2)=\\ =-0.0408-\frac{0+0.0408}{-9-0.034}\cdot(0.034)=-0.0408\\ |p_4-p_3|=0\\ x=-0.0408


a0=0,b0=1f(a0)=f(0)=9f(b0)=f(1)=230+18+92219=27p2=a0b0a0f(b0)f(a0)f(a0)==01027+9(9)=0.25a1=0.25,b1=1f(a1)=f(0.25)==230(0.25)4+18(0.25)3++9(0.25)2221(0.25)9=62.508f(b1)=f(1)=27p3=a1b1a1f(b1)f(a1)f(a1)==0.2510.2527+62.508(62.508)=0.771p3p2=0.521a2=0.771,b2=1f(a2)=f(0.771)==230(0.771)4+18(0.771)3++9(0.771)2221(0.771)9=84.519f(b2)=f(1)=27p4=a2b2a2f(b2)f(a2)f(a2)==0.77110.77127+84.519(84.519)=0.945p4p3=0.174a_0=0, b_0=1\\ f(a_0)=f(0)=-9\\ f(b_0)=f(1)=230+18+9-221-9=27\\ p_2=a_0-\frac{b_0-a_0}{f(b_0)-f(a_0)}f(a_0)=\\ =0-\frac{1-0}{27+9}\cdot(-9)=0.25\\ a_1=0.25, b_1=1\\ f(a_1)=f(0.25)=\\ =230(0.25)^4+18(0.25)^3+\\ +9(0.25)^2-221(0.25)-9=-62.508\\ f(b_1)=f(1)=27\\ p_3=a_1-\frac{b_1-a_1}{f(b_1)-f(a_1)}f(a_1)=\\ =0.25-\frac{1-0.25}{27+62.508}\cdot(-62.508)=0.771\\ |p_3-p_2|=0.521\\ a_2=0.771, b_2=1\\ f(a_2)=f(0.771)=\\ =230(0.771)^4+18(0.771)^3+\\ +9(0.771)^2-221(0.771)-9=-84.519\\ f(b_2)=f(1)=27\\ p_4=a_2-\frac{b_2-a_2}{f(b_2)-f(a_2)}f(a_2)=\\ =0.771-\frac{1-0.771}{27+84.519}\cdot(-84.519)=0.945\\ |p_4-p_3|=0.174\\

a3=0.945,b3=1f(a3)=f(0.945)==230(0.945)4+18(0.945)3++9(0.945)2221(0.945)9=11.194f(b3)=f(1)=27p5=a3b3a3f(b3)f(a3)f(a3)==0.94510.94527+11.194(11.194)=0.961p5p4=0.016a_3=0.945, b_3=1\\ f(a_3)=f(0.945)=\\ =230(0.945)^4+18(0.945)^3+\\ +9(0.945)^2-221(0.945)-9=-11.194\\ f(b_3)=f(1)=27\\ p_5=a_3-\frac{b_3-a_3}{f(b_3)-f(a_3)}f(a_3)=\\ =0.945-\frac{1-0.945}{27+11.194}\cdot(-11.194)=0.961\\ |p_5-p_4|=0.016\\

a4=0.961,b4=1f(a4)=f(0.961)==230(0.961)4+18(0.961)3++9(0.961)2221(0.961)9=0.929f(b4)=f(1)=27p6=a4b4a4f(b4)f(a4)f(a4)==0.96110.96127+0.929(0.929)=0.962p6p5=0.001x=0.962a_4=0.961, b_4=1\\ f(a_4)=f(0.961)=\\ =230(0.961)^4+18(0.961)^3+\\ +9(0.961)^2-221(0.961)-9=-0.929\\ f(b_4)=f(1)=27\\ p_6=a_4-\frac{b_4-a_4}{f(b_4)-f(a_4)}f(a_4)=\\ =0.961-\frac{1-0.961}{27+0.929}\cdot(-0.929)=0.962\\ |p_6-p_5|=0.001\\ x=0.962

b)

f(x)=230x4+18x3+9x2221x9f(x)=920x3+54x2+18x221an+1=anf(an)f(an)a0=1f(1)=433f(1)=920+5418221=1105a1=a0f(a0)f(a0)=14331105=0.608f(a1)=f(0.608)==230(0.608)4+18(0.608)3++9(0.608)2221(0.608)9=156,079f(a1)=f(0.608)==920(0.608)3+54(0.608)2++18(0.608)221=418.757a2=a1f(a1)f(a1)=0.608156.079418.575=0.235a2a1=0.373f(x)=230x^4+18x^3+9x^2-221x-9\\ f'(x)=920x^3+54x^2+18x-221\\ a_{n+1}=a_n-\frac{f(a_n)}{f'(a_n)}\\ a_0=-1\\ f(-1)=433\\ f'(-1)=-920+54-18-221=-1105\\ a_1=a_0-\frac{f(a_0)}{f'(a_0)}=-1-\frac{433}{-1105}=-0.608\\ f(a_1)=f(-0.608)=\\ =230(-0.608)^4+18(-0.608)^3+\\ +9(-0.608)^2-221(-0.608)-9=156,079\\ f'(a_1)=f'(-0.608)=\\ =920(-0.608)^3+54(-0.608)^2+\\ +18(-0.608)-221=-418.757\\ a_2=a_1-\frac{f(a_1)}{f'(a_1)}=-0.608-\frac{156.079}{-418.575}=-0.235\\ |a_2-a_1|=0.373

f(a2)=f(0.235)==230(0.235)4+18(0.235)3++9(0.235)2221(0.235)9=43.9f(a2)=f(0.235)==920(0.235)3+54(0.235)2++18(0.235)221=234.187a3=a2f(a2)f(a2)=0.23543.9234.187=0.0448a3a2=0.19f(a_2)=f(-0.235)=\\ =230(-0.235)^4+18(-0.235)^3+\\ +9(-0.235)^2-221(-0.235)-9=43.9\\ f'(a_2)=f'(-0.235)=\\ =920(-0.235)^3+54(-0.235)^2+\\ +18(-0.235)-221=-234.187\\ a_3=a_2-\frac{f(a_2)}{f'(a_2)}=-0.235-\frac{43.9}{-234.187}=-0.0448\\ |a_3-a_2|=0.19

f(a3)=f(0.0448)==230(0.0448)4+18(0.0448)3++9(0.0448)2221(0.0448)9=0.918f(a3)=f(0.0448)==920(0.0448)3+54(0.0448)2++18(0.0448)221=221.78a4=a3f(a3)f(a3)=0.04480.918221.78=0.0401a4a3=0.0047x=0.0401f(a_3)=f(-0.0448)=\\ =230(-0.0448)^4+18(-0.0448)^3+\\ +9(-0.0448)^2-221(-0.0448)-9=0.918\\ f'(a_3)=f'(-0.0448)=\\ =920(-0.0448)^3+54(-0.0448)^2+\\ +18(-0.0448)-221=-221.78\\ a_4=a_3-\frac{f(a_3)}{f'(a_3)}=-0.0448-\frac{0.918}{-221.78}=-0.0401\\ |a_4-a_3|=0.0047\\ x=-0.0401

a0=1f(a0)=f(1)==230+18+92219=27f(a0)=f(1)==920+54+18221=771a1=a0f(a0)f(a0)=127771=0.965a_0=1\\ f(a_0)=f(1)=\\ =230+18+9-221-9=27\\ f'(a_0)=f'(1)=\\ =920+54+18-221=771\\ a_1=a_0-\frac{f(a_0)}{f'(a_0)}=1-\frac{27}{771}=0.965\\

f(a1)=f(0.965)==230(0.965)4+18(0.965)3++9(0.965)2221(0.965)9=1.743f(a1)=f(0.965)==920(0.965)3+54(0.965)2++18(0.965)221=673.398a2=a1f(a1)f(a1)=0.9651.743673.398=0.962a2a1=0.003x=0.962f(a_1)=f(0.965)=\\ =230(0.965)^4+18(0.965)^3+\\ +9(0.965)^2-221(0.965)-9=1.743\\ f'(a_1)=f'(0.965)=\\ =920(0.965)^3+54(0.965)^2+\\ +18(0.965)-221=673.398\\ a_2=a_1-\frac{f(a_1)}{f'(a_1)}=0.965-\frac{1.743}{673.398}=0.962\\ |a_2-a_1|=0.003\\ x=0.962


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