# in A level FM, why is it that a straight line has pi radians?

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#1
can someone also explain what a radian acctually is?
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1 year ago
#2
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1 year ago
#3
Radians are just a measure of angle like degrees. There are 2pi radians in a circle, or 360 degrees. Thus pi radians = 180 degrees, a straight line.
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1 year ago
#4
I didnt do fm, but I did get an A in normal maths this year.

a radian is a measure of an angle, just like degrees. to get from degrees to radian you multiply by π and divide by 180. and from radian to degrees is multiply by 180 and divide by π.

so 1π = 180*

since a straight line is straight, it has an angle of 180, so π rad
Last edited by JJJJJAAAAMES; 1 year ago
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1 year ago
#5
One radian is the angle created when the corresponding arc is of length one radius.
its slightly less than 60 degrees.

In a sense, defining an angle in terms of a known length makes more sense than a fairly arbitrary split into 360 degrees.
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1 year ago
#6
Not sure I understand the question "why is it that a straight line has pi radians?", but I can explain what a radian is.

If you have a sector of a circle (like a piece of cake) where the arc length (ie the curved edge) is the same length as the straight side(s), equal to radius of course, then the angle subtended from the centre of the circle is defined as 1 radian.

Other replies explain how to convert between degrees and radians which is what you will need to know.
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1 year ago
#7
(Original post by Azimbrook1)
can someone also explain what a radian acctually is?
2pi radians equals 360 degrees. At some level it's as simple as that.

However there are good reasons to work with radians.

In geometry the circumference of a circle is 2 pi r and the length of an arc is r x angle, but only if the angle is measured in radians.

In calculus, the derivative of sinx is cosx, but only if you're working with radians. The correct formula when using degrees would be much more messy. Similarly the usual Taylor series that define sinx and cosx work when you're using radians.
Last edited by RichE; 1 year ago
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1 year ago
#8
I believe you're talking about polar coordinates? Where the Initial Line is marked and Pi is marked as a vertical line?
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