In: Advanced Math
Find a root of an equation f(x)=5x3-3x2+8 initial solution x0=-0.81, using Newton Raphson method
Approximate root of the equation 5x3-3x2+8=0 Let f(x)=5x3-3x2+8
ddx(5x3-3x2+8)=15x2-6x
∴f′(x)=15x2-6x
x0=-0.81
1st iteration :
f(x0)=f(-0.81)=5⋅(-0.81)3-3⋅(-0.81)2+8=3.3745
f′(x0)=f′(-0.81)=15⋅(-0.81)2-6⋅(-0.81)=14.7015
x1=x0-f(x0)f′(x0)
x1=-0.81-3.374514.7015
x1=-1.0395
2nd iteration :
f(x1)=f(-1.0395)=5⋅(-1.0395)3-3⋅(-1.0395)2+8=-0.8587
f′(x1)=f′(-1.0395)=15⋅(-1.0395)2-6⋅(-1.0395)=22.4467
x2=x1-f(x1)f′(x1)
x2=-1.0395--0.858722.4467
x2=-1.0013
3rd iteration :
f(x2)=f(-1.0013)=5⋅(-1.0013)3-3⋅(-1.0013)2+8=-0.0269
f′(x2)=f′(-1.0013)=15⋅(-1.0013)2-6⋅(-1.0013)=21.0461
x3=x2-f(x2)f′(x2)
x3=-1.0013--0.026921.0461
x3=-1
4th iteration :
f(x3)=f(-1)=5⋅(-1)3-3⋅(-1)2+8=0
f′(x3)=f′(-1)=15⋅(-1)2-6⋅(-1)=21.0001
x4=x3-f(x3)f′(x3)
x4=-1-021.0001
x4=-1
Approximate root of the equation 5x3-3x2+8=0 is -1
root is-1