NCERT Class XI Mathematics - Straight Lines - Solutions
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Question : 37
Total: 74
Reduce the following equations into normal form. Find their perpendicular distances from the origin and angle between perpendicular and the positive x-axis.
(i) x −√ 3 y + 8 = 0,
(ii) y –2 = 0,
(iii) x – y = 4.
(i) x −
(ii) y –2 = 0,
(iii) x – y = 4.
Solution:
(i) Given equation is x − √ 3 y + 8 = 0
⇒ x −√ 3 y = −8
⇒ − x +√ 3 y = 8 ... (1)
Also,√ ( coeff . of x 2 ) + ( coeff . of y 2 )
=√ ( − 1 ) 2 + ( √ 3 ) 2 = √ 1 + 3 = √ 4 = 2
Now dividing both the sides of (1) by 2, we get −
x +
y = 4
⇒ – cos 60°x + sin 60° y = 4.
⇒ {cos (180° – 60°)} x + {sin (180° – 60°)}y = 4
⇒ cos 120° x + sin 120° y = 4
∴ x cos 120° + y sin 120° = 4 is the required equation in normal form
Straight Lines 179
Since The normal form is x cosω + y sinω = p
So, ω = 120° and p = 4
∴ Distance of the line from origin is 4 and the angle between perpendicular and positive x-axis is 120°.
(ii) Given equation is y – 2 = 0
⇒ y = 2 ⇒ 0 . x + 1 . y = 2
⇒ x cos 90° + y sin 90° = 2 is the required equation in normal form
Since The normal form is x cosω + y sinω = p So, ω = 90° and p = 2
∴ Distance of the line from origin is 2 and the angle between perpendicular and positive x-axis is 90°.
(iii) Given equation is x – y = 4 ... (1)
Also√ ( coeff . of x 2 ) + ( coeff . of y 2 )
=√ ( 1 ) 2 ( − 1 ) 2 = √ 1 + 1 = √ 2
Now dividing both the sides of (1) by√ 2 , we get
−
= 2 √ 2
⇒ x cos 45° − y sin 45° = 2√ 2
⇒ x cos (360° - 45°) + y sin (360° - 45°) =2 √ 2
⇒ x cos 315° + y sin 315° = 2√ 2 ,
is the required equation in normal form.
Q The normal form is x cosω + y sinω = p
So, p = 2√ 2 and ω = 315°
∴ Distance of the line from the origin is 2 2 and the angle between
perpendicular and the positive x-axis is 315°.
⇒ x −
⇒ − x +
Also,
=
Now dividing both the sides of (1) by 2, we get −
⇒ – cos 60°x + sin 60° y = 4.
⇒ {cos (180° – 60°)} x + {sin (180° – 60°)}y = 4
⇒ cos 120° x + sin 120° y = 4
∴ x cos 120° + y sin 120° = 4 is the required equation in normal form
Straight Lines 179
Since The normal form is x cosω + y sinω = p
So, ω = 120° and p = 4
∴ Distance of the line from origin is 4 and the angle between perpendicular and positive x-axis is 120°.
(ii) Given equation is y – 2 = 0
⇒ y = 2 ⇒ 0 . x + 1 . y = 2
⇒ x cos 90° + y sin 90° = 2 is the required equation in normal form
Since The normal form is x cosω + y sinω = p So, ω = 90° and p = 2
∴ Distance of the line from origin is 2 and the angle between perpendicular and positive x-axis is 90°.
(iii) Given equation is x – y = 4 ... (1)
Also
=
Now dividing both the sides of (1) by
⇒ x cos 45° − y sin 45° = 2
⇒ x cos (360° - 45°) + y sin (360° - 45°) =
⇒ x cos 315° + y sin 315° = 2
is the required equation in normal form.
Q The normal form is x cosω + y sinω = p
So, p = 2
∴ Distance of the line from the origin is 2 2 and the angle between
perpendicular and the positive x-axis is 315°.
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