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Graphing Polynomials Practice Problems

A polynomial sketch needs four pieces of information and no table of values. These twelve problems drill each piece separately — the y-intercept, what happens at each zero, the turning-point limit — and then run the whole thing backwards, recovering a formula from a described graph.

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MPhil in Mathematics, Founder of Mathovia
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Graphing Polynomials Practice Problems

The graphing polynomials lesson reduces sketching to five steps. These twelve problems drill the individual pieces, then combine them in the last few — including the reverse direction, where you recover a formula from a described graph.

The five steps

StepWhat you do
1End behavior from the degree and leading coefficient
2Zeros from the factored form
3Multiplicity at each zero — odd crosses, even touches
4-intercept from
5Join smoothly and check the turning-point count

What multiplicity does at the axis

Between consecutive zeros the sign cannot change, because a polynomial can only move from positive to negative by passing through zero. So once you know the sign on one interval, the multiplicities determine it everywhere else.

Running it backwards

Given a graph, build the factors from the zeros and set each exponent from the behaviour there:

Then use one extra known point to pin down . The zeros alone can never give you — every vertical stretch of the same curve crosses the axis in exactly the same places, which is why these questions always supply an intercept or a labelled point.

Frequently Asked Questions

What do I need before I can sketch a polynomial?+

Four things: the end behavior from the leading term, the zeros from the factored form, the multiplicity at each zero, and the y-intercept from P(0). Those fix both tails, every axis crossing and the vertical position, which is enough to draw the curve.

How do I find the y-intercept quickly?+

Evaluate P(0). If the polynomial is written out in standard form, that is just the constant term — no work at all. If it is factored, substitute zero into every bracket and multiply.

What is the difference between crossing and touching?+

It is decided by multiplicity. An odd multiplicity crosses the axis; an even multiplicity touches it and turns back. A multiplicity of 3 still crosses, but visibly flattens as it does.

How many turning points should my sketch have?+

At most n − 1 for degree n. It can have fewer, but never more, so counting the turns in your sketch is a quick way to catch an error. A cubic drawn with three turns is definitely wrong.

Why can a sketch not give exact turning point heights?+

Because locating them needs calculus — you set the derivative to zero. A sketch gets every zero, every tail and the y-intercept exactly right, and the peak heights only approximately, which is all a sketch is for.

How do I write a polynomial from its graph?+

Turn each zero into a factor, with the exponent set by whether the graph crosses or touches. That gives the shape up to a constant. Then substitute one other known point, usually the y-intercept, and solve for the leading coefficient a.

More practice problems