A right triangle contains a right angle, so it must have two sides that are perpendicular. If the slopes of two sides can be shown to be negative reciprocals of each other, then it can be concluded that a right angle is formed. If a triangle contains a right angle, then it is a right triangle.
He needed to divide instead of subtracting it on the last step.
Answer:

Step-by-step explanation:
Pythagorean theorem is:


Answer:
surface area: 7241.25
Step-by-step explanation:
using this formula for surface area of cyclinder: 2πrh+2π
diameter = 2r --> 39.2 = 2r
so r= 19.6