Question

Find a degree 4 polynomial having zeros -8,-1,4 and 5 and the coefficient of x^4 equal 1.

Answer 1

Answer:

  x^4 -53x^2 +108x +160

Step-by-step explanation:

If a is a zero, then (x-a) is a factor. For the given zeros, the factors are ...

  p(x) = (x +8)(x +1)(x -4)(x -5)

Multiplying these out gives the polynomial in standard form.

  = (x^2 +9x +8)(x^2 -9x +20)

We note that these factors have a sum and difference with the same pair of values, x^2 and 9x. We can use the special form for the product of these to simplify our working out.

  = (x^2 +9x)(x^2 -9x) +20(x^2 +9x) +8(x^2 -9x) +8(20)

  = x^4 -81x^2 +20x^2 +180x +8x^2 -72x +160

  p(x) = x^4 -53x^2 +108x +160

_____

The graph shows this polynomial has the required zeros.