then how many negative values can z take ?a)Noneb)Onec)Twod)Threee)A f...
To Find: Number of negative values of z
Approach:
- Solve the given equation
- Note that the denominator is z - 1.
- To remove the denominator, we will need to multiply each term of this equation with z - 1.
- This will be time consuming (because we will have to multiply each term with z as well as with -1. Example:
and is likely to result in a tedious calculation. - To simplify this process, we will substitute (z - 1) as x
- Find the value of z
- Count the number of negative values of z
Substitute z - 1 = x
Therefore z = x + 1 ; z - 2 = x -1
Hence
This is a cubic equation (involves x3) and you may feel that you do not know how to solve a cubic equation.
However, before giving up, think about how you solve a quadratic equation? By rewriting the given equation into its factors.
Let’s try if the cubic equation above can be similarly written into factors. We’ll find that the middle term, -21x, can be broken down as under:

That is
- z - 1 = 1 or 4 or -5
- z = 2 or 5 or -4
- Thus, we get three values of z. However, the question asks specifically about the number of negative values of z.
- Among the 3 possible values of z, we see that only one value of z is negative.
Correct Answer: Option B
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