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Home  >>  CBSE XI  >>  Math  >>  Straight Lines
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Choose the correct answer from the given four options. The equation of the line passing through the point (1, 2) and perpendicular to the line $x+y+1 = 0 $ is

$\begin {array} {1 1} (A)\;y – x + 1 = 0 & \quad (B)\;y – x – 1 = 0 \\ (C)\;y – x + 2 = 0 & \quad (D)\;y – x – 2 = 0 \end {array}$

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Toolbox:
  • The slope of a line perpendicular to a given line where slope is $'m'$ is $ - \large\frac{1}{m}$.
Step 1 :
Equation of the given line is
$x+y+1=0$
Slope of this line is -1.
Equation of the required line which is perpendicular to the above line is
$x-y+k=0$
This line passes through the point (1,2)
$ \therefore 1-2+k=0$
$ \Rightarrow k-1=0$ or $ k=1$
Hence equation of the required line is
$x-y+1=0$
Hence B is the correct option.
answered Jul 3, 2014 by thanvigandhi_1
 

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