Page 40 - Mathematics Class - XI

Viva-Voce

1. What is meant by argand plane?
Ans. The plane having a complex number assigned to each of its point is called the complex plane or the argand
plane.
2. What do you understand by complex number?

Ans. A number of the form a + ib, where a and b are real numbers, is called a complex number. Here, a is called
the real part and ib is called the imaginary part of the complex number.
3. Who was the first mathematician to introduce the symbol i (iota)?
Ans. Euler was the first mathematician to introduce the symbol i.

4. Find the value of i and i .
134
19
Ans. i = i = –1 [⸪ 134 leaves remainder as 2 when it is divided by 4.]
134
2
i = i = –i [⸪ 19 leaves remainder as 3 when it is divided by 4.]
3
19
5. What is the additive inverse of 3 + 2i?
Ans. The additive inverse of a number is the number multiplied by –1. Therefore, the additive inverse of 3 + 2i
is –3 –2i.

MCQs

1. The length of the line segment which meets the point (–1, – i) and (–2, –3i) is
a) –5 b) 15 c) 5 d) 25
z 1
2. If 1, then the locus of z is
zi
a) an ellipse b) a circle c) a line d) a parabola
i
3. The argument of the complex number 2 2 is

i
a) p b) c) p d) p
4 4 12 2

4. If z = 1−i 3 , then the value of org. (z) will be
1+i 3
a) 60° b) 120° c) 240° d) 300°
9
5. If 1 i 3 aib then the value of b is

a) 1 b) 256 c) 0 d) 9 3

6. 2. 3 ?
a) 6 b) − 6 c) i 6 d) None of these

p
Answers: 1. c) 5 2. c) a line 3. d) 4. c) 240° 5. c) 0 6. b) − 6
2
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