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Find the angle between the lines y = (2-3)(x+5) and y = (2+3)(x-7)

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Question

Find the angle between the lines y = `(2 - sqrt(3)) (x + 5)` and y = `(2 + sqrt(3))(x - 7)`

Sum
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Solution

The given equations are y = `(2 - sqrt(3))(x + 5)`  .....(i)

And y = `(2 + sqrt(3))(x - 7)`  ...(ii)

Slope of equation (i) m1 (say) = `(2 - sqrt(3))`

And slope of equation (ii) m2 (say) = `(2 + sqrt(3))`

Let θ be the angle between the two given lines

∴ tan θ =  `|(m_1 - m_2)/(1 + m_1m_2)|`

= `|(2 - sqrt(3) - 2 - sqrt(3))/(1 + (2 - sqrt(3))(2 + sqrt(3)))|`

= `|(-2sqrt(3))/(1 + 4 - 3)|`

= `|(-2sqrt(3))/2|`

= `|- sqrt(3)|`

⇒ tan θ = `sqrt(3)` or `- sqrt(3)`

∴ θ = 60° or 120°

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Chapter 10: Straight Lines - Exercise [Page 178]

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NCERT Exemplar Mathematics Exemplar [English] Class 11
Chapter 10 Straight Lines
Exercise | Q 3 | Page 178

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