MP Board Class 11th Maths Important Questions Chapter 5 Complex Numbers and Quadratic Equations

MP Board Class 11th Maths Important Questions Chapter 5 Complex Numbers and Quadratic Equations

MP Board Class 11th Maths Important Questions Chapter 5 Complex Numbers and Quadratic Equations

Relations and Functions Objective Type Questions

(A) Choose the correct option :

Question 1.
If x + iy = 2 + 3i, then (x, y) will be :
(a) (3, 2)
(b) (2, 3)
(c) (- 2,- 3)
(d) (3, 3)
Answer:
(b) (2, 3)

Question 2.
The simplest form of
(a) – i
(b) i
(c) ± i
(d) None of these.
Answer:
(b) i

Question 3.
If z is a complex number, then z + z is :
(a) Real number
(b) Imaginary number
(c) Nothing can be said
(d) None of these.
Answer:
(a) Real number

Question 4.

Question 5.
Number of solution of the equation z + z = 0 is :
(a) 1
(b) 2
(c) 3
(d) 4
Answer:
(d) 4

Question 6.
Argument of complex number 0 is :
(a) 0
(b) π
(c) 2π
(d) Not defined
Answer:
(d) Not defined

Question 7.

Question 8.
Argument (z₁.z₂) = ………………
(a) arg (z₁) – arg (z₂)
(b) arg (z₁) + arg (z₂)
(c) arg (z₁). arg (z₂)
(d) None of these
Answer:
(b) arg (z₁) + arg (z₂)

Question 9.
The least positive integer n for which  is :
(a) 2
(b) 4
(c) 8
(d) 12
Answer:
(b) 4

Question 10.

(B) Match the following :

Answer:

1. (d)
2. (a)
3. (f)
4. (b)
5. (c)
6. (e)

(c) Fill in the blanks :

(D) Write true / false :

Answer:

1. True
2. False
3. False
4. True
5. True
6. False.

(E) Write answer in one word / sentence :

Complex Numbers and Quadratic Equations Very Short Answer Type Questions

Question 1.
If 1, ω, ω² are the cube root of unity then find the value of ω³ⁿ.
Solution:
Since ω³ = 1
ω³ⁿ = (ω³)ⁿ = (1)ⁿ = 1.

Question 2.
Find the value of i⁴ⁿ.
Solution:
i⁴ⁿ = (i⁴)ⁿ = (i².i²)ⁿ = [(- 1)(- 1)]ⁿ = (1)ⁿ = 1.

Question 3.
Find the condition of two complex numbers x + iy and a + ib are compaired.
Solution:
If x + iy = a + ib
Then, x = a, y = b.

Question 4.
Write conjugate of a complex number z = a – ib.
Solution:
z = conjugate of a – ib = a – (- ib)
= a + ib.

 

Question 5.
Write the complex number – 6₃ in ordered form.
Solution:
Ordered form of z = a + ib is (a, b).
Given: z = 0 – 6i
Ordered pair (0, – 6).

Question 9.
Write (1 – i)⁴ in form of a + ib.
Solution:
(1 – i)⁴ = [ (1 – i)² ]² (NCERT)
= [1 + i² – 2i]² = [1 – 1 – 2i]², [∵ i² = – 1]
= (- 2i)² = 4i² = 4(- 1) = – 4
= – 4 + 0i.

Question 15.
Write the triangle inequality for the two complex number Z₁ and z₂.
Solution:
| Z₁| and | z₂| are the two sides of any triangle
Then, | z₀ + z₂| ≤ | z₁| +| z₂|

Question 16.
If T and 9 are the modulus and argument of the complex number a + ib, then write its polar form.
Solution:
Polar form of a + ib is r(cosθ + i sinθ).

Question 17.
If z = cosθ + i sinθ where |z| = 1, then find 1/z.
Solution:
1/z = cosθ – isinθ.

Question 18.
Write the statement of De – moivre’s theorem.
Solution:
If polar form of z = a + ib is r(cosθ + isinθ), then De – moivre’s theorem is
(cosθ + isinθ)n = cos nθ + i sin nθ.

Question 19.
Write polar form of i.
Solution:
a + ib = 0 + i. 1

Question 20.
Find the polar form of (- 2 + 2i).
Solution:

Complex Numbers and Quadratic Equations Long Answer Type Questions

Question 1.

Question 2.

Question 3.
Write (5 – 3i)³ in the form of a + ib.
Solution:
(5 – 3i)³ = (5)³ – (3i)³ – 3(5².3i) + 3.5(3i)²
= 125 – 27.i³ – 75.3i + 15.9i²
= 125 – 27i.i² – 225i + 15(- 9)
= 125 + 27i – 225i – 135
= – 10 – 198i.

Find the multiplicative inverse of following complex number :

Question 4.
4 – 3i
Solution:
Let the multiplicative inverse of 4 – 3i is a + ib.
Then, (4 – 3i) x (a + ib) = 1

Question 5.

Question 6.
Find the polar form of the following :

Solution:

Now, let – 1 + i = r(cosθ + i sinθ),
Then, r cosθ = – 1 …. (1)
and r sinθ = 1 …. (2)
Squaring and adding equation (1) and (2),
r² = 1 + 1 = 2
⇒ r = √2
Put value of r in equation (1) and (2),

Comparing the real and imaginary parts,
r cosθ = – 1
r sinθ = 1

Squaring and adding equation (1) and (2),

∵ Real part is negative and imaginary part is positive of z, hence θ will lie in 4^th quadrant

Question 7.
Find modulus and argument of complex number z = – 1 – i√3 (NCERT)
Solution:
Let z = – 1 – i√3 = rcosθ + ir sinθ

Comparing the real and imaginary parts,
rcosθ = – 1 …. (1)
rsinθ = – 3–√ …. (2)
Squaring and adding equation (1) and (2),

Since both the real and imaginary part of z are negative.
∴ θ lies in third quadrant

Question 8.
Find the modulus and argument of z = – √3+ i.
Solution:
Let z = – √3 + i = rcosθ + ir sinθ

Comparing the real and imaginary parts,
r cosθ = – √3
rsinθ = 1
Squaring and adding eqns. (1) and (2),
rcosθ = – √3 …. (1)
rsinθ = 1 …. (2)
Squaring and adding equation (1) and (2),

Since both the real and imaginary part of z are negative and positive respectively.
∴ θ lies in 2^2nd quadrant

Question 9.
Find the modulus and argument of 1 – i.
Solution:
Let z = 1 – i = rcosθ + ir smθ
Comparing the real and imaginary parts,
1 = r cosθ
and – 1 = rsinθ
Squaring and adding equation (1) and (2),
(1)² + (- 1)² = r² cos²0 + r² sin²0
⇒ r²(cos²0 + sin²0) = 1 + 1,
⇒ r²= 2 ⇒ r = √2 (modulus)
Dividing equation (2) by equation (1),

Question 10.
Find square root of complex number 3 + 4i.
Solution:

On squaring,
3 + 4 i = (x + iy)²
⇒ 3 + 4i = x² + 2ixy + i²y²
⇒ 3 + 4i = x² + 2ixy – y²
⇒ 3 + 4i = (x² – y²) + i(2xy)
x² – y² = 3 …. (1)
2xy = 4 …. (2)
(x² + y²)² = (x² – y²)² + 4x²y²
= (3)² + (4)²
= 25
∴ x² + y² = 5 …. (3)
Now adding eqns. (1) and (3),
2x² = 8
⇒ x² = 4
⇒ x = ± 2
From equation (2), 2(± 2)y = 4
∴ y = ± 1

Question 11.
Find square root of complex number 8 – 6i.
Solution:

On squaring,
8 – 6i = (x + iy)²
⇒ 8 – 6i = x² + 2ixy + i²y² .
⇒ 8 – 6i = (x² – y²) + 2ixy
∴ 8 = x² – y² …. (1)
and – 6 = 2 xy …. (2)
(x² + y²)² = (x² – y²)² + 4x²y²
(x²+y²)² = (8)² + (- 6)²
= 64 + 36 = 100
∴ x² + y² = 10 …. (3)
Now adding equation (1) and (3),
2x² = 18
⇒ x² = 9
⇒ x = ±3
From equation (3), y² = 10 – 9 = 1
∴ y = ± 1

Question 12.
x² + 3x + 9 = 0.
Solution:
Given : x² + 3x + 9 = 0
Comparing the above equation by ax² + bx + c = 0,
a = 1, b = 3, c = 9
Now, D = b² – 4ac
= 3² – 4 x 1 x 9 = 9 – 36 = – 27 < 0

Question 13.
– x² + x – 2 = 0.
Solution:
Given : – x² + x – 2 = 0
Comparing the above equation by ax² + bx + c = 0,

Question 14.
x² + 3x + 5 = 0.
Solution:
Given : x² + 3x + 5 = 0
Comparing the above equation by ax² + bx+c = 0,
a = 1, b = 3, c = 5

Question 15.
x² – x + 2 = 0
Solution:
Given : x² – x + 2 = 0
Comparing the above equation by ax² + bx + c = 0,
a = 1, b = – 1, c = 2
Now, D = b² – 4ac
= (- 1)² – 4 x 1 x 2 = 1 – 8 = – 7 < 0

Question 16.
If  = 1, then And the minimum positive integer number of m. (NCERT)
Solution: