# NCERT Class 11-Math's: Chapter –5 Complex Numbers and Quadratic Equations Part 4

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**Question 8:**

If are complex numbers such that

, then find the value of

**Answer:**

Given that

**Question 9:**

If a complex number *z* lies in the interior or on the boundary of a circle of radius 3 units and centre , find the greatest and least values of

**Answer:**

Distance of the point representing from the centre of the circle is

According to given condition .

Now

Therefore, greatest value of is .

Since least value of the modulus of a complex number is zero, the least value of

**Question 10:**

Locate the points for which

**Answer:**

which is the interior of circle with centre at origin and radius 4 units, and which is exterior of circle with centre at origin and radius 3 units. Hence is the portion between two circles and .

**Question 11:**

Find the value of when

**Answer:**

Therefore

**Question 12:**

Find the value of P such that the difference of the roots of the equation is

**Answer:**

Let be the roots of the equation

Therefore

Now

Therefore

**Question 13:**

Find the value of *a* such that the sum of the squares of the roots of the equation is least.

**Answer:**

Let be the roots of the equation

Therefore, and

Now

Therefore, will be minimum if

**Question 14:**

Find the value of *k* if for the complex numbers

**Answer:**

L. H. S.

R. H. S.

Hence, equating LHS and RHS, we get .