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

- 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.

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