How do you reflect a shape across x=-1

Question

I am really struggling with this question and it isn't quite making sense. Please help and if you don't mind answering quickly.

Reflection across $x = −1$

$H(−3, −1), F(2, 1), E(−1, −3)$.

Answer 1

The process of reflection of a shape S about a line L is very simple.

For every point of S draw a line meeting L perpendicularly. Then extend this line equally further and stop. The point where you stopped is the reflected image of the point you started with.

Do this for every point of S.

Alternatively think of the plane as a sheet of paper. Draw your figure S with wet ink. Now fold this plane making the line L as crease. This causes points on either side of line to come into contact with each other. Now unfold to restore. The wet ink would have made impression . And this impression is the reflection of S.

Answer 2

Reflecting P(p, q) about L : x = a, we get the image at P’(t, q) for some t to be determined.

Let M = (a, q) be a point on the L and at the same level as P and P’.

Note that the line L acts as a mirror so that P and P’ (at the back of the mirror) are equidistance from it. In other words, M is the midpoint of P and P’. Applying the midpoint formula, we get $\dfrac { t + p }{2} = a$. Solving it, we get the formula quoted by @EvanAad.