Question

Please solve Q. no. 18 (c). Its important for me.
Ans. in my book = x+y+1=0

Answer 1

18) c.   Reflection like it happens in a plane mirror.
       For better understanding draw a rough sketch of the points and the mirror lines on paper. (like it's done on a graph sheet). See diagram.
      
    Image of point  A(3, -4) = A'(x1, y1) when reflected in the line x+2 = 0.
    Mirror line is:  x = -2.
    Light ray perpendicular to mirror x = -2 is parallel to x axis, and passes through A(3,-4).  So the light ray is:  y = -4. 
    Point of incidence on the mirror line will be:  Q(-2, -4).
    A'Q = QA = 3 - (-2) = 5.
    So  A' = (-2 - 5 , -4) = (-7,-4).
    It can be found also by taking Q as the midpoint of two points A and A'.

    2nd Mirror line : y = 1.  So the ray from A' (-7, -4) is perpendicular to the mirror line, and passes through A'.  It is parallel to y axis,  x = -7.
    Distance A' R  of A' from mirror line = 1 - (-4) = 5.
    R is the point of incidence of the ray from A' on the mirror line y = 1.
    So A"R = RA' = 5.
    A" is above the mirror line of y = 1.
    A" = (-7,  1 + 5) = (-7, 6)

Equation of line through A=(3,-4) and (A" = (-7, 6)
    slope = (6 -(-4)) / (-7 - 3) = -1
    (y - 6) / (x -(- 7)) = -1
     y + x + 1 = 0     Answer

Answer 2

y+x+1=0 is the answer for your question
OK my dear friend