Ex 10.1, 10 - Chapter 10 Class 11 Straight Lines (Term 1)

Last updated at Feb. 3, 2020 by Teachoo

Transcript

Ex 10.1, 10
Find the angle between the x-axis and the line joining the points (3, –1) and (4, –2).
First we find slope of line joining the points (3, –1) and (4, –2).
We know that slope of line passing through (x1, y1) and (x2, y2) is
m = (𝑦_2 − 𝑦_1)/(𝑥_2 − 𝑥_1 )
Here x1 = 3, y1 = –1
& x2 = 4, y2 = –2
Slope of line joining (3, –1) and (4, –2) is
m = ( −2 − (−1))/(4 − 3)
= ( − 2 + 1)/(4 − 3) = ( − 1)/1 = –1
Ex 10.1, 10
Find the angle between the x-axis and the line joining the points (3, –1) and (4, –2).
First we find slope of line joining the points (3, –1) and (4, –2).
We know that slope of line passing through (x1, y1) and (x2, y2) is
m = (𝑦_2 − 𝑦_1)/(𝑥_2 − 𝑥_1 )
Here x1 = 3, y1 = –1
& x2 = 4, y2 = –2
Slope of line joining (3, –1) and (4, –2) is
m = ( −2 − (−1))/(4 − 3)
= ( − 2 + 1)/(4 − 3) = ( − 1)/1 = –1
= ( −2 + 1)/(4 − 3)
= ( −1)/1
= –1
Now,
Finding Angle from Slope
Now,
Slope = m = tan θ
where θ is the angle between line and positive x-axis
So,
m = tan θ
–1 = tan θ
tan θ = –1
tan θ = tan (135°)
θ = 135°
So, Required angle = θ = 135°
Rough
Ignoring signs
tan θ = 1
So, θ = 45°
As tan is negative
∴ θ will lie in 2nd quadrant,
So, θ = 180° – 45°
= 135°

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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