Question #113260
Using the Horner’s method find the values of f(4) and f'(4) for the polynomial
f(x) = x^4 +2x^3 −x^2 +1.
1
Expert's answer
2020-05-01T18:02:30-0400

ANSWER: f(4)=369,f(4)=344f(4)=369, f'(4)=344

EXPLANATION:

f(x)=a4x4+a3x3+a2x2+a1x+a0=x4+2x3x2+1f(x)=a_4x^4+a_3x^3+a_2x^2+a_1x+a_0=x^4+2x^3-x^2+1

To calculate f(4)f(4) , we represent the polynomial ff in the form f(x)=(x4)(b3x3+b2x2+b1x+b0)+rf(x)=(x-4)(b_3x^3+b_2x^2+b_1x+b_0)+ r , using the Horner's method.

b3=a4,bk1=4bk+ak,k=3,2,1,r=4b0+a0{ b }_{ 3 }={ a }_{ 4 },\quad { b }_{ k-1 }=4{ b }_{ k }+a_{ k },\quad k=3,2,1,\quad r=4{ b }_{ 0 }+{ a }_{ 0 }


Thus, we obtain b3=1b2=41+2=6b1=461=23{ b }_{ 3 }=1\rightarrow { b }_{ 2 }=4\cdot 1+2=6\quad \rightarrow { b }_{ 1 }=4\cdot 6-1=23\rightarrow

b0=423+0=r=492+1=369,r=f(4)\rightarrow { b }_{ 0 }=4\cdot 23+0=\rightarrow r=4\cdot 92+1=369, r=f(4)

Similarly: f(x)=4x3+6x22x  =a3x3+a2x2+a1x+a0=f'(x)={ 4x }^{ 3 }{ +6x }^{ 2 }-2{ x }^{ \ \ }=a_3x^3+a_2x^2+a_1x+a_0= =(x4)(b2x2+b1x+b0)+r=(x-4)(b_2x^2+b_1x+b_0)+ r

b2=4b1=44+6=22b0=4222=86{ b }_{ 2 }=4\rightarrow { b }_{ 1}=4\cdot4+6=22\quad \rightarrow { b }_{ 0 }=4\cdot 22 -2=86\rightarrow

=r=486+0=344,r=f(4)=344=\rightarrow r=4\cdot 86+0=344, r=f'(4)=344


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