Peter is making an "X marks the spot" flag for a treasure hunt. The flag is made of a square white flag with sides of 121212 centimeters. He will make the "X" by stretching red ribbon diagonally from corner to corner.
How many centimeters of ribbon will Peter need to make the "X"?

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

circle area = pi * radius^2

if diameter = 10 then radius = 5

circle area = pi * 5^2

circle area = pi * 25

circle area = 78.5398163397 square units

step-by-step explanation:

boxplot