The Pythagorean theorem is a^2 + b^2 = c^2. You use it when solving for the sides of a triangle.
The term (2 + 8) is described as the total amount of pieces of fabric. It makes it easier to put this term this way so you wouldn't have to do (8 x 5) + (2 x 5) and do the distributive property.
1. BC/CD = AC/CE 1. Given
2. <BCA is congruent to <ECD 2. Vertical angles are congruent
3. Tr.ACB is congr to Tr.ECD 3. SAS Similarity
3sqrt(2)
You can either use Pythagorean theorem or special triangle proportions to find the side that is parallel to z. Since in a 45-45-90 degree triangle, the hypotenuse is the leg times the square root of 2, and the hypotenuse is 3, we know that the leg is 3/sqrt(2) which is equal to 3 sqrt(2) / 2. Since z is twice this length, we know that z is equal to 2 x 3sqrt(2)/2 = 3sqrt(2)
