Given coordinates of the triangle:
(3,4)
(4,7)
(8,2).
We are given rule for transformation: (x,y) --> (-x,y).
According to given rule the y coordinates remain same but the coordinates of x's getting multiplied by a negative sign.
Let us write transformed coordinates of the given triangle according to given rule.
(3,4) --> (-3,4)
(4,7) --> (-4,7)
(8,2) --> (-8,2).
Now, we can plot those transformed coordinates on the graph and plot transformed triangle.