Notice that A lies on the line y = 7 since its coordinates are (5,7), meaning that its y-coordinate is 7.

Since y = 7 is the line of symmetry, and A is one of the vertices of the △and lies on this line,

the line divides the △ into two identical parts.

this means that B is a reflection of C about the line y = 7. Basically mirror images of each other , where the line is like the 'mirror'


So C and B are equidistant from the line y = 7

Since y = 7 is a horizontal line and B(-3,9) ,

in order to be the mirror image of B about this line, C must have the same x-coordinate as B, which is -3.


Vertical distance from B to the line
= 9 - 7
= 2 units

So B is 2 units vertically above the line and this means C is 2 units vertically below the line.


y-cooridinate of C = 7 - 2 = 5

Coordinates of C are (-3,5)