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Contents - Student subdomain for University of Bath

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Chapter 3<br />

Polynomial Equations<br />

In the first parts <strong>of</strong> this chapter, we will deal with polynomial equations, either<br />

singly or as sets <strong>of</strong> equations. A preliminary remark is in order. Any polynomial<br />

equation<br />

A = B, (3.1)<br />

where A and B are polynomial equations, can be reduced to one whose righthand<br />

side is zero, i.e.<br />

A − B = 0. (3.2)<br />

Notation 15 Hence<strong>for</strong>th, all polynomial equations will be assumed to be in the<br />

<strong>for</strong>m <strong>of</strong> (3.2).<br />

3.1 Equations in One Variable<br />

We may as well assume that the unknown variable is x. If the equation is linear<br />

in x then, by the notation above, it takes the <strong>for</strong>m<br />

The solution is then obvious: x = −b/a.<br />

3.1.1 Quadratic Equations<br />

ax + b = 0. (3.3)<br />

Again, by the notation above, our equation takes the <strong>for</strong>m<br />

ax 2 + bx + c = 0. (3.4)<br />

The solutions are well-known to most schoolchildren: there are two <strong>of</strong> them, <strong>of</strong><br />

the <strong>for</strong>m<br />

x = −b ± √ b 2 − 4ac<br />

. (3.5)<br />

2a<br />

55

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