The first 3 are correct but for the last one I’m not sure
You just need to plug those expressions inside the formula: it doesn't matter if they're expressions involving a variable instead of plain numbers: the formula becomes

If you want, you can simplify it by expanding the square and then multiply the two parenthesis:

Answer:
A. It has reflectional symmetry
B. It is symmetrical
D. It has five lines of symmetry
Step-by-step explanation:
we know that
A regular pentagon has 5 sides and 5 lines of symmetry. The number of lines of symmetry in a regular polygon is equal to the number of sides
Every regular polygon has reflectional symmetry
Regular polygons are symmetrical
therefore
A. It has reflectional symmetry ------> Is true
B. It is symmetrical -----> Is true
C. It has exactly one line of symmetry ----> Is false
D. It has five lines of symmetry -----> Is true
I believe it is C, but correct me if I'm wrong.