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Published on: 20/09/2019
Polynomials
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1.
Factorise \(x^3+13x^2+32x+20\)
2.
Factorise \(x^3-2x^2-x+2\)
3.
Factorise \({ 3 }x^{ 2 }-x-4\)
4.
Determine which of the following polynomials has (x+1) a factor: \({ x }^{ 3 }-{ x }^{ 2 }-(2+\sqrt { 2 } )x+\sqrt { 2 } .\)
5.
Determine which of the following polynomials has (x+1) a factor: \(x^4+3x^3+3x^2+x+1\)
6.
Find the remainder when \(x^3+3x^2+3x+1\) is divided by \(x+\pi\)
7.
Find the remainder when \(x^3+3x^2+3x+1\) is divided by \(x\)
8.
Verify whether the following are zeroes of the polynomial, indicated against them.
\(p(x)={ 3x }^{ 2 }-1,x=-\frac { 1 }{ \sqrt { 3 } } ,\frac { 2 }{ \sqrt { 3 } } \)
9.
Find p(0), p(1) and p(2) for each of the following polynomials:
p(x) = (x - 1) (x + 1)
10.
Find p(0), p(1) and p(2) for each of the following polynomials:
p(x) = x3
11.
Classify the following as linear, quadratic and cubic polynomials:
r2
12.
Write the degree of the following polynomials:
5x3 + 4x2 + 7x
13.
Write the coefficients of x2 in the following:
2 + x2 + x
14.
Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer.
\({ 4x }^{ 2 }-3x+7\)
1.
\(x^3+13x^2+32x+20\)
Let \(p(x)={ x }^{ 3 }+13{ x }^{ 2 }+32x+20\)
By trail, we find that
\(p(-1)={ (-1) }^{ 3 }+13{ (-1) }^{ 2 }+32(-1)+20\)
\(=-1+13-32+20=0\)
\(\therefore\) By Factor Theorem, x-(-1), i.e., (x+1) is a factor of p(x).
Now,
\({ x }^{ 3 }+13{ x }^{ 2 }+32x+20={ x }^{ 2 }(x+1)+12x(x+1)+20(x+1)\)
\(=(x+1)({ x }^{ 2 }+12x+20)\)
\(=(x+1)({ x }^{ 2 }+2x+10x+20)\)
\(=(x+1)\{ x(x+2)+10(x+2)\} \)
\(=(x+1)(x+2)(x+10).\)
2.
Let \(p(x)={ x }^{ 3 }-2{ x }^{ 2 }-x+2\)
By trail, we find that
\(p(1)={ (1) }^{ 3 }-2{ (1) }^{ 2 }-(1)+2\)
\(=1-2-1+2=0\)
\(\therefore \) By Factor Theorem, (x-1) is a factor of p(x).
Now,
\({ x }^{ 3 }-2{ x }^{ 2 }-x+2={ x }^{ 2 }(x-1)-x(x-1)-2(x-1)\)
\(=(x-1)({ x }^{ 2 }-x-2)\)
\(=(x-1)({ x }^{ 2 }-2x+x-2)\)
\(=(x-1)\{ x(x-2)+1(x-2)\} \)
\(=(x-1)(x-2)(x+1).\)
3.
\({ 3 }x^{ 2 }-x-4\)
\({ 3 }x^{ 2 }-x-4={ 3 }x^{ 2 }-4x+3x-4\)
\(=x(3x-4)+1(3x-4)\)
\(=(3x-4)(x+1)\)
4.
\({ x }^{ 3 }-{ x }^{ 2 }-(2+\sqrt { 2 } )x+\sqrt { 2 } .\)
Let \(p(x)=\)\({ x }^{ 3 }-{ x }^{ 2 }-(2+\sqrt { 2 } )x+\sqrt { 2 } .\)
The zero of x+1 is -1
\(p(-1)=(-1)^{ 3 }+3(-1)^{ 2 }+(2-\sqrt { 2 } )(-1)+\sqrt { 2 }\)
\( \\ =-1-1+2+\sqrt { 2 } +\sqrt { 2 } =2\sqrt { 2 } \neq 0\)
\(\therefore\) By factors theorem, x+1 is not a factor of \({ x }^{ 3 }-{ x }^{ 2 }-(2+\sqrt { 2 } )x+\sqrt { 2 } .\)
5.
\(x^4+3x^3+3x^2+x+1\)
Let \(p(x)=\)\(x^4+3x^3+3x^2+x+1\)
The zero of x+1 is -1.
\(p(-1)=(-1)^4+3(-1)^3+(3-1)^2+(-1)+1\)
\(\\ =1-3+3-1+1=1\neq 0\)
\(\therefore\) By factors theorem, x+1 is not a factor of \(x^4+3x^3+3x^2+x+1\)
6.
\(x+\pi\)
\(x+\pi=0\ d\Rightarrow\ x=-\pi\)
\(\therefore\) Remainder \(= (-\pi)^3+3(-\pi)^2+3(-\pi)+1\)
\(= -\pi^3+3\pi^2+3\pi+1\)
7.
\(x\)
\(\therefore\) Remainder
\(= (0)^3+3(0)^2+3(0)+1=1\)
8.
\(p\left( -\frac { 1 }{ \sqrt { 3 } } \right) =3\left( \frac { 1 }{ \sqrt { 3 } } \right) ^{ 2 }-1\)
\(\\ \ =3\left( \frac { 1 }{ 3 } \right) -1=1-1=0\)
\(\\ p\left( \frac { 2 }{ \sqrt { 3 } } \right) =3\left( \frac { 2 }{ \sqrt { 3 } } \right) ^{ 2 }-1=3\left( \frac { 4 }{ 3 } \right) -1\)
\(\\ \ =4-1=3\neq 0\)
\(\therefore -\frac { 1 }{ \sqrt { 3 } } \) is a zero of p(x) but \(\frac { 2 }{ \sqrt { 3 } } \) is not a zero of p(x)
9.
\(\therefore \ p(0)=(0-1)(0+1)=(-1)(1)=-1\)
\(\\ p(1)=(1-1)(1+1)=(0)(2)=0\)
and \(p(2)=(2-1)(2+1)=(1)(3)=3\)
10.
\(\therefore \ p(0)={ (0) }^{ 3 }=0,\)
\(p(1)={ (1) }^{ 3 }=1\)
and \(p(2)={ (2) }^{ 3 }=8\)
11.
quadratic
12.
Term with the highest power of x = 5x3
Exponent of x in this term = 3
Therefore Degree of this polynomial = 3
13.
Coefficient of x2 = 1
14.
This expression is a polynomial in one variable x because in the expression there is only one variable (x) and all the indices of x are whole numbers.
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