Given:
The leading coefficient of a polynomial is 8.
Polynomial roots are 1 and 2.
The graph passes through the point (4,5).
To find:
The 3rd root and the equation of the polynomial.
Solution:
The factor form of a polynomial is:
[tex]y=a(x-c_1)(x-c_2)...(x-c_n)[/tex]
Where, a is a constant and [tex]c_1,c_2,...,c_n[/tex] are the roots of the polynomial.
Polynomial roots are 1 and 2. So, [tex](x-1)[/tex] and [tex](x-2)[/tex] are the factors of the polynomial.
Let the third root of the polynomial by c, then [tex](x-c)[/tex] is a factor of the polynomial.
The leading coefficient of a polynomial is 8. So, a=8 and the equation of the polynomial is:
[tex]y=8(x-1)(x-2)(x-c)[/tex]
The graph passes through the point (4,5). Putting [tex]x=4,y=5[/tex], we get
[tex]5=8(4-1)(4-2)(4-c)[/tex]
[tex]5=8(3)(2)(4-c)[/tex]
[tex]5=48(4-c)[/tex]
Divide both sides by 48.
[tex]\dfrac{5}{48}=4-c[/tex]
[tex]c=4-\dfrac{5}{48}[/tex]
[tex]c=\dfrac{192-5}{48}[/tex]
[tex]c=\dfrac{187}{48}[/tex]
Therefore, the 3rd root on the polynomial is [tex]\dfrac{187}{48}[/tex].
