Please help Describe a way that you can remember the elements of the reflection matrices if you forget where the 1s, -1s, and 0s belong.

Step-by-step explanation:

Multiplying the vertex matrix with the matrix gives us a reflection matrix. The most common matrix reflections are seen as reflection in the x - axis as well as reflection in the y - axis.  

It can also be reflect by  90 degree or by 180 degree.

So, one way to remember the elements is by multiplying the given matrix by a unit matrix. And on the other hand you can remember the elements remembering by what degree we are reflecting the matrix. This way makes it easier to remember the elements.

answer: 8 years

step-by-step explanation:

the explanation is that in 8 years the child will be 20 and in 8 years the father will be 40 and 20 is half of 40.