Polynomials-Exercise 2.1
Maths - Exercise
Q1. The graphs of y = p(x) are given in Fig. 2.10 below, for some polynomials p(x). Find the number of zeroes of p(x), in each case.
- In figure (i), \(p(x)\) neither crosses nor touches the \(x\)-axis. Therefore, p(x) has no \(x\) for which \(p(x)\)=0.
- In figure (ii) \(px\) crosses \((x)\)-axis once. Therefore, there is exactly one real zero of \(p(x)\)
- In figure (iii) \(p(x)\) crosses \(x\)-axis three times. Thus \(p(x)\) has three distinct real zeros.
- In fig (iv) \(p(x)\) crosses \(x\)-axis two times. Therfore, there exist two zeros of \(p(x)\)
- In fig (v) \(p(x)\) crosses \(x\)-axis 4 times. Therfore, \(p(x)\) has four real zeros.
- In fig (vi) \(p(x)\) crosses \(x\)-axis once nd touches twice(i.e., has two points of tangency). Therefore, there are three real zeros of \(p(x)\)
Notes/Explanations:
- When a graph crosses the \(x\)-axis, the zero is a simple root.
- When it touches but does not cross the \(x\)-axis (tangent), it is a repeated root (even multiplicity).
- The total number of times the graph crosses or touches the \(x\)-axis (counting multiplicity) gives the number of real zeros.