Question

James wants to draw a line diagonally across a rectangular piece of paper. If the paper measures 9 inches by 12 inches, what is the minimum length of the straight-edge he needs to make the line?

Answer 1

The straight-edge would have to be 12.7279220614 inches

Answer 2

If James draws a diagonal line of length x from one right angle to the opposite right angle, then he divides his piece of paper into two pieces, each of them is right triangle with legs 9 inches and 12 inches.
By Pythagorean theorem:
 $x^2=9^2+12^2 \\ x^2=81+144 \\ x^2=225 \\ x=15$ inches.
Answer: 15 inches