# Triangular shaft change to circular shaft

1. Jan 3, 2017

### fonseh

1. The problem statement, all variables and given/known data
for the circular cross section shaft , why we need to put an sin60 as to get the area ?

2. Relevant equations

3. The attempt at a solution
why the area shouldnt be pi(0.004) ^2 only ?

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2. Jan 3, 2017

### BvU

The author doesn't. This sine appears in the calculation of the area of the triangular shaft
Nothing ?
That's not an attempt at solution. Where do you see this value ? I don't even see it appearing anywhere. All I see is $\pi c^2$ which is a reasonable expression for the area of a circle with radius $c$.

3. Jan 3, 2017

### Staff: Mentor

The author is calculating the area of the equilateral triangle, using ½×base×height

He then equates this area to that of a circle of radius c and is able to calculate the value of c.