Answer:
3√3
Step-by-step explanation:
Taking just the face that includes both P and y, we have a triangle with a base of 6 and a slant of 6. Py is the perpendicular bisector of this base; this gives us a smaller right triangle with a leg of 6/2 = 3 and a hypotenuse of 6. Using the Pythagorean theorm,
3²+b²=6²
9+b² = 36
Subtract 9 from each side:
9+b²-9 = 36-9
b² = 27
Take the square root of each side:
√(b²) = √27
b = √(3*3*3) = √(3²*3) = 3√3
