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Math Practice

End Behavior Practice Problems

End behavior comes from two facts and nothing else: whether the degree is even or odd, and whether the leading coefficient is positive or negative. These twelve problems drill that pair, including the cases where you have to find the leading term yourself from a factored or rearranged expression.

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MPhil in Mathematics, Founder of Mathovia
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End Behavior Practice Problems

The end behavior lesson reduces the whole topic to a two-by-two table. These twelve problems drill it, with the harder ones requiring you to work out the leading term yourself before the table applies.

The four cases

DegreeLeading coefficientLeft tailRight tail
evenpositiveupup
evennegativedowndown
oddpositivedownup
oddnegativeupdown

Finding the leading term without expanding

For a factored polynomial, multiply only the leading term of each factor:

Degree 5, coefficient . That is everything the table needs, and it took one line instead of expanding a quintic.

Watch for a factor written backwards. has leading term , not , and it flips the sign of the whole leading coefficient. Rewriting it as before you start makes the minus sign impossible to miss.

Turning points as a check

A degree-6 polynomial can turn at most five times. This does not affect the tails, but it catches a sketch that has the right end behavior and an impossible middle.

Frequently Asked Questions

What determines a polynomial's end behavior?+

Only two things: whether the degree is even or odd, and the sign of the leading coefficient. Every other term is irrelevant, because as x grows large the leading term dominates everything else by an arbitrarily wide margin.

What are the four possible cases?+

Even degree with a positive lead sends both tails up. Even with a negative lead sends both down. Odd with a positive lead goes down on the left and up on the right. Odd with a negative lead does the reverse.

How do I find the leading term of a factored polynomial?+

Multiply the leading terms of each factor together and ignore everything else. For (x − 1)(x + 2)(x − 3) that is x · x · x = x³. You never need to expand the whole product just to read end behavior.

What if a factor is written as (2 − x) instead of (x − 2)?+

Its leading term is −x, so it contributes a factor of −1 to the leading coefficient. This is the most common way an end-behavior answer comes out backwards, and it is worth rewriting such a factor as −(x − 2) before you start.

Do turning points affect end behavior?+

No — they are a separate feature of the middle of the graph. But the turning-point limit of n − 1 is a useful cross-check, because a sketch with too many wiggles is wrong regardless of whether the tails are right.

Why does the constant term never matter?+

Because it does not grow. At x = 1000 a constant of 7 is negligible against a leading term in the billions. End behavior is a statement about limits, and only the fastest-growing term survives it.

More practice problems