NCERT Solutions for Class 11 Maths Chapter 5
Complex Numbers and Quadratic Equations Class 11
Chapter 5 Complex Numbers and Quadratic Equations Exercise 5.1, 5.2, 5.3, miscellaneous Solutions
Exercise 5.1 : Solutions of Questions on Page Number : 103
Express the given complex number in the form a + ib:
Q2 :
Answer :
Express the given complex number in the form a + ib: i-39
Q4 :
Answer :
Express the given complex number in the form a + ib: (1 - i) - (-1 + i6)
Q6 :
Answer :
Express the given complex number in the form a + ib:
Q8 :
Answer :
Express the given complex number in the form a + ib:
Q10 :
Answer :
Find the multiplicative inverse of the complex number 4 - 3i
Let z = 4 – 3i
Then, = 4 + 3i and
Therefore, the multiplicative inverse of 4 – 3i is given by
Find the multiplicative inverse of the complex number
Let z =
Therefore, the multiplicative inverse of is given by
Find the multiplicative inverse of the complex number -i
Let z = –i
Therefore, the multiplicative inverse of –i is given by
Express the following expression in the form of a + ib.
Exercise 5.2 : Solutions of Questions on Page Number : 108
Find the modulus and the argument of the complex number
On squaring and adding, we obtain
Since both the values of sin θand cos θ are negative and sinθand cosθare negative in III quadrant,
Find the modulus and the argument of the complex number
On squaring and adding, we obtain
Convert the given complex number in polar form: 1 - i
1 – i
Let rcos θ = 1 and rsin θ = –1
On squaring and adding, we obtain
This is the
Convert the given complex number in polar form: - 1 + i
– 1 + i
Let rcos θ = –1 and rsin θ = 1
On squaring and adding, we obtain
It can be written,
Convert the given complex number in polar form: - 1 - i
– 1 – i
Let rcos θ = –1 and rsin θ = –1 On squaring and adding, we obtain
This is the
Convert the given complex number in polar form: -3
–3
Let rcos θ = –3 and rsin θ = 0
On squaring and adding, we obtain
Convert the given complex number in polar form:
Let rcos θ = and rsin θ = 1
On squaring and adding, we obtain
Convert the given complex number in polar form: i
i
Let rcosθ = 0 and rsin θ = 1
On squaring and adding, we obtain
Exercise 5.3 : Solutions of Questions on Page Number : 109
Solve the equation x2 + 3 = 0
The given quadratic equation is x2 + 3 = 0
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = 1, b = 0, and c = 3
Therefore, the discriminant of the given equation is D = b2 – 4ac = 02 – 4 × 1 × 3 = –12 Therefore, the required solutions are
Solve the equation 2x2 + x + 1 = 0
The given quadratic equation is 2x2 + x + 1 = 0
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = 2, b = 1, andc = 1
Therefore, the discriminant of the given equation is D = b2 – 4ac = 12 – 4 × 2 × 1 = 1 – 8 = –7 Therefore, the required solutions are
Solve the equation x2 + 3x + 9 = 0
The given quadratic equation is x2 + 3x + 9 = 0
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = 1, b = 3, and c = 9
Therefore, the discriminant of the given equation is D = b2 – 4ac = 32 – 4 × 1 × 9 = 9 – 36 = –27 Therefore, the required solutions are
Solve the equation -x2 + x - 2 = 0
The given quadratic equation is –x2 + x – 2 = 0
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = –1, b = 1, and c = –2
Therefore, the discriminant of the given equation is
D = b2 – 4ac = 12 – 4 × (–1) × (–2) = 1 – 8 = –7 Therefore, the required solutions are
Solve the equation x2 + 3x + 5 = 0
The given quadratic equation is x2 + 3x + 5 = 0
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = 1, b = 3, and c = 5
Therefore, the discriminant of the given equation is D = b2 – 4ac = 32 – 4 × 1 × 5 =9 – 20 = –11 Therefore, the required solutions are
Solve the equation x2 - x + 2 = 0
The given quadratic equation is x2 – x + 2 = 0
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = 1, b = –1, and c = 2
Therefore, the discriminant of the given equation is
D = b2 – 4ac = (–1)2 – 4 × 1 × 2 = 1 – 8 = –7 Therefore, the required solutions are
Solve the equation
The given quadratic equation is
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = , b = 1, and c =
Therefore, the discriminant of the given equation is
D = b2 – 4ac = 12 – = 1 – 8 = –7 Therefore, the required solutions are
Solve the equation
The given quadratic equation is
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = , b = , and c =
Therefore, the discriminant of the given equation is
D = b2 – 4ac =
Therefore, the required solutions are
Solve the equation
The given quadratic equation is This equation can also be written as
On comparing this equation with ax2 + bx + c = 0, we obtain
a = , b = , and c = 1
Therefore, the required solutions are
Solve the equation
The given quadratic equation is This equation can also be written as
On comparing this equation with ax2 + bx + c = 0, we obtain
a = , b = 1, and c =
Therefore, the required solutions are
Exercise Miscellaneous : Solutions of Questions on Page Number : 112
Evaluate:
Q2 :
Answer :
Reduce to the standard form.
Q4 :
Answer :
Convert the following in the polar form:
Answer :
(i) Here,
Let r cos θ = –1 and r sin θ = 1 On squaring and adding, we obtain r2 (cos2 θ + sin2 θ) = 1 + 1
⇒ r2 (cos2 θ + sin2 θ) = 2
⇒ r2 = 2 [cos2 θ + sin2 θ = 1]
∴z = r cos θ + i r sin θ
This is the required polar form.
(ii) Here,
Let r cos θ = –1 and r sin θ = 1 On squaring and adding, we obtain
r2 (cos2 θ + sin2 θ) = 1 + 1
⇒r2 (cos2 θ + sin2 θ) = 2
⇒ r2 = 2 [cos2 θ + sin2 θ = 1]
∴z = r cos θ + i r sin θ
Solve the equation
The given quadratic equation is This equation can also be written as
On comparing this equation with ax2 + bx + c = 0, we obtain
a = 9, b = –12, and c = 20
Therefore, the discriminant of the given equation is
D = b2 – 4ac = (–12)2 – 4 × 9 × 20 = 144 – 720 = –576
Solve the equation
The given quadratic equation is This equation can also be written as
On comparing this equation with ax2 + bx + c = 0, we obtain
a = 2, b = –4, and c = 3
Therefore, the discriminant of the given equation is
D = b2 – 4ac = (–4)2 – 4 × 2 × 3 = 16 – 24 = –8 Therefore, the required solutions are
Solve the equation 27x2 - 10x + 1 = 0
The given quadratic equation is 27x2 – 10x + 1 = 0
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = 27, b = –10, and c = 1
Therefore, the discriminant of the given equation is
D = b2 – 4ac = (–10)2 – 4 × 27 × 1 = 100 – 108 = –8
Solve the equation 21x2 - 28x + 10 = 0
The given quadratic equation is 21x2 – 28x + 10 = 0
On comparing the given equation with ax2 + bx + c = 0, we obtain
a = 21, b = –28, and c = 10
Therefore, the discriminant of the given equation is
D = b2 – 4ac = (–28)2 – 4 × 21 × 10 = 784 – 840 = –56
Therefore, the required solutions are
If find .
Q11 :
Answer :
If a + ib = , prove that a2 + b2 =
On comparing real and imaginary parts, we obtain
Let . Find
(i)
(ii) On comparing imaginary parts, we obtain
Find the modulus and argument of the complex number .
Let , then
On squaring and adding, we obtain
Find the real numbers x and y if (x - iy) (3 + 5i) is the conjugate of -6 - 24i.
Let
It is given that,
Equating real and imaginary parts, we obtain
Multiplying equation (i) by 3 and equation (ii) by 5 and then adding them, we obtain
Putting the value of x in equation (i), we obtain
Thus, the values of x and y are 3 and –3 respectively.
Find the modulus of .
Q17 :
If (x + iy)3 = u + iv, then show that .
On equating real and imaginary parts, we obtain
If α and β are different complex numbers with = 1, then find . Answer :
Let α = a + ib and β = x + iy
Find the number of non-zero integral solutions of the equation .
If (a + ib) (c + id) (e + if) (g + ih) = A + iB, then show that (a2 + b2) (c2 + d2) (e2 + f2) (g2 + h2) = A2 + B2.
On squaring both sides, we obtain
(a2 + b2) (c2 + d2) (e2 + f2) (g2 + h2) = A2 + B2
If , then find the least positive integral value of m.
Therefore, the least positive integer is 1.
Thus, the least positive integral value of m is 4 (= 4 × 1).