A spiral staircase turns 270 degrees as it rises 10 feet. The radius of the staircase is 3 feet. What is the number of feet in the length of the handrail? Express your answer as a decimal to the nearest tenth.

Lightning Feb 3, 2019

#1**+1 **

The easiest way to see this is to imagine that we can "unfold" the spiral to create a rectangle

The bottom side of the rectangle is just the arc length of a circle of a radius of 3 ft turned through 270°= (3/4) of a whole revolution....in other words.....(3/4) (2pi) (3) = (9/2)pi ft = 4.5 pi ft

The side of the rectangle will be rise of the staircase = 10ft

And the diagonal of the rectangle will be the length of the handrail

We can use the Pythagorean Theorem to solve this

handrail length = √ [ (4.5 pi)^2 + 10^2 ] ≈ 17.3 ft

CPhill Feb 3, 2019