Answer:
approximately 6.708 feet
Step-by-step explanation:
We use the Pythagorean theorem to solve the problem, using 3 feet and 6 feet as the legs of a right angle triangle. The diagonal of the screen is therefore the "hypotenuse" of this right angle triangle, and can be determined via the formula:
[tex]diagonal = \sqrt{(3\,ft)^2+(6\,ft)^2} \\diagonal = \sqrt{9\,ft^2+36\,ft^2} \\diagonal = \sqrt{45} \,ft\\diagonal = 3\,\sqrt{5} \,ft[/tex]
which is approximately 6.708 feet