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Q: If the arc length of a sector in the unit circle is 4.2 what is the measure of the angle of the sector?

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It is found by: (sector area/entire circle area) times 360 in degrees

The radian measure IS the arc length of the unit circle, by definition - that is how the radian is defined in the first place.

If you're only given the length of the arc, then you can't. You also need to know the fraction of the circle that's in the sector. You can figure that out if you know the angle of the arc, or the radius or diameter of the circle. -- Diameter of the circle = 2 x (radius of the circle) -- Circumference of the circle = (pi) x (Diameter of the circle) -- (length of the arc)/(circumference of the circle) = the fraction of the whole circle that's in the sector or -- (degrees in the arc)/360 = the fraction of the whole circle that's in the sector -- Area of the circle = (pi) x (radius of the circle)2 -- Area of the sector = (Area of the circle) x (fraction of the whole circle that's in the sector)

Angle is dimensionless. It's actually the ratio of two lengths ... the length of an arc of the circle to the length of the radius of the circle. That ratio is the same number for the same angle in any-size circle, and it's directly proportional to the angle that cuts the arc. When you measure angles in radians, the angle IS that number.

Well...a "sector" is part of a circle...which has a radius. But in order to calculate the radius, you'd need both the total area of the circle, and the central angle of the sector (or enough information to get the central angle). Let's say you're looking at a clock (and let's assume both the minute hand and the hour hand are the same length, and extend from the center all the way to the edge of the clock). Assuming this, the length of both hands would be the radius, as they are segments whose endpoints are the center of the circle, and a point on the circle. If you put the hands of the clock at the 12 and 3, you've just created a sector that is 1/4 of the entire area. The angle created by these hands would have a vertex that is the center of the circle...and this would be the "central angle"...and it would have a measure of 1/4 of 360...which is 90. But...while you can say what "fraction" of the circle is encompassed by the sector, you can't do any calculations until you have somewhere to start from. Let's say in the above example, you knew that the entire area of the circle was 64pi. The radius of that circle would be the square root of 64=8. This would, obviously be the radius of the sector as well...but since our "central angle" was 90...the AREA of the sector is 90/360 (or 1/4) of the total area. Since our initial area was 64pi...the area of the sector would be 16pi. But if all you want is a simple formula, the radius of a circle (and by extension the sector), given the area of the sector (s) and the measure of the central angle (c) would be the square root of [(360*s)/(c*pi)]

Related questions

Area of sector/Area of circle = Angle of sector/360o Area of sector = (Area of circle*Angle of sector)/360o

There is no direct relation between the area of a sector and the length of an arc. You must know the radius (or diameter) or the angle of the sector at the centre.

Length of arc = angle of arc (in radians) × radius of circle With a ratio of 7:8 the area of the sector is 7/8 the area of the whole circle. This is the same as saying that the circle has been divided up into 8 equal sectors and 7 have been shaded in. Dividing the circle up into 8 equal sectors will give each sector an angle of arc of 2π × 1/8 7 of these sectors will thus encompass an angle of arc of 2π × 1/8 × 7 = 2π × 7/8 = 7π/4 Thus the length of the arc of the sector is 7π/4 × radius of the circle. --------------------------------- Alternatively, it can be considered that as 7/8 of the area is in the sector, the length of the arc is 7/8 the circumference of the circle = 7/8 × 2π × radius = 7π/4 × radius.

6.5

The angle measure is: 90.01 degrees

It is found by: (sector area/entire circle area) times 360 in degrees

It depends on what else is known about the sector: length of arc, area or some other measure.

The radian measure IS the arc length of the unit circle, by definition - that is how the radian is defined in the first place.

If you're only given the length of the arc, then you can't. You also need to know the fraction of the circle that's in the sector. You can figure that out if you know the angle of the arc, or the radius or diameter of the circle. -- Diameter of the circle = 2 x (radius of the circle) -- Circumference of the circle = (pi) x (Diameter of the circle) -- (length of the arc)/(circumference of the circle) = the fraction of the whole circle that's in the sector or -- (degrees in the arc)/360 = the fraction of the whole circle that's in the sector -- Area of the circle = (pi) x (radius of the circle)2 -- Area of the sector = (Area of the circle) x (fraction of the whole circle that's in the sector)

Multiply ( pi R2 ) by [ (angle included in the sector) / 360 ].

-- Circumference of the circle = (pi) x (radius) -- length of the intercepted arc/circumference = degree measure of the central angle/360 degrees

Angle is dimensionless. It's actually the ratio of two lengths ... the length of an arc of the circle to the length of the radius of the circle. That ratio is the same number for the same angle in any-size circle, and it's directly proportional to the angle that cuts the arc. When you measure angles in radians, the angle IS that number.