How do you describe the end behavior for f(x)=-x^5+4x^3-5x-4?

1 Answer
Oct 29, 2016

As xrarr-oo, f(x)rarr oo
As xrarroo, f(x)rarr -oo

Explanation:

f(x)=color(blue)(-1)x^color(red)5 +4x^3-5x-4

End behavior is determined by the degree of the polynomial and the leading coefficient (LC).

The degree of this polynomial is the greatest exponent, or color(red)5.

The leading coefficient is the coefficient of the term with the greatest exponent, or color(blue)(-1).

For polynomials of even degree, the "ends" of the polynomial graph point in the same direction as follows.

Even degree and positive LC:
As xrarr-oo, f(x)rarr oo
As xrarr oo, f(x)rarr oo

Even degree and negative LC:
As xrarr-oo, f(x)rarr -oo
As xrarroo, f(x)rarr -oo

For polynomials of odd degree, the "ends" of the polynomial graph point in opposite directions as follows (note, there is a saying that Odd means Opposite when graphing).

Odd degree and positive LC:
As xrarr-oo, f(x)rarr -oo
As xrarr oo, f(x)rarr oo

Odd degree and negative LC:
As xrarr-oo, f(x)rarr oo
As xrarroo, f(x)rarr -oo

In this example, the degree is odd and the leading coefficient is negative. Therefore,
As xrarr-oo, f(x)rarr oo
As xrarroo, f(x)rarr -oo