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A square of side a lies above the x- axis  and has one vertex at the origin. The side passing through the origin makes an angle \alpha (0< \alpha < \pi /4)   with the positive direction of  x- axis. The equation of its diagonal not passing through the origin is

  • Option 1)

    y(\cos \alpha +\sin \alpha )+x(\sin \alpha -\cos \alpha )=a

  • Option 2)

    y(\cos \alpha +\sin \alpha )+x(\sin \alpha +\cos \alpha )=a

  • Option 3)

    y(\cos \alpha +\sin \alpha )+x(\cos \alpha - \sin \alpha )=a

  • Option 4)

    y(\cos \alpha -\sin \alpha )-x(\sin \alpha -\cos \alpha )=a

 

Answers (1)

best_answer

As we learnt in

Two – point form of a straight line -

y-y_{1}=\left ( \frac{y_{2}-y_{1}}{x_{2}-x_{1}} \right )(x-x_{1})

 

- wherein

The lines passes through  (x_{1}y_{1})  and  (x_{2}\, y_{2})

 

 

Slope of a line -

If \Theta is the angle at which a straight line is inclined to a positive direction of x-axis, then the slope is defined by

m= \tan \Theta.

- wherein

 

 Equation of diagonal AB is 

\left ( y-a \sin\alpha \right )= \left ( \frac{a \cos \alpha-a sin\alpha }{-a \sin \alpha - a \cos \alpha} \right ) (x- a \cos \alpha )

\Rightarrow y (\sin \alpha + \cos \alpha) + x (\cos \alpha - \sin \alpha) = 0

 

 


Option 1)

y(\cos \alpha +\sin \alpha )+x(\sin \alpha -\cos \alpha )=a

Incorrect

Option 2)

y(\cos \alpha +\sin \alpha )+x(\sin \alpha +\cos \alpha )=a

Incorrect

Option 3)

y(\cos \alpha +\sin \alpha )+x(\cos \alpha - \sin \alpha )=a

Correct

Option 4)

y(\cos \alpha -\sin \alpha )-x(\sin \alpha -\cos \alpha )=a

Incorrect

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Aadil

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