What Is The Meaning Of Pie? In Geometry... Example C=pie D=pie(50)

The word is pi, not pie.  It is the ratio of the radius of a circle to its circumference.  Circumference is C, D is the diameter, which equals 2 x the radius (R)
It is equal to 22/7, or 3.14159......
Now, C (circumference) = piD  or C = 2piR

You should use quotation marks when writing a book chapter. Example. "First Sight" "Open Book"  "Confessions"

Because Joe isn't good at keeping secrets, he may tell others , and your secret will be out.

Although it was raining, Sarah stood outside, and she got wet.

Since Maria was angry, we decided we should leave her alone, but Ralph kept bugging her.

Because we were out of eggs, my mother had to go to the store, but she forgot her wallet.