Defining the arc length about a circle

In this lesson fine look at arcs the circles and also how to find their measure.

You are watching: Find the measure of arc db


Anarcis component of the circumference of a circle. There are three species of arcs.

Minor arcsare much less than ???180^circ???.

Major arcsare an ext than ???180^circ???.

Semi-circle arcsare precisely ???180^circ???.



Measures that arcs and main angles

Thecentral angleof an arc is the angle that connects both end of the arc and has a vertex in ~ the facility of the circle. The central angle and the arc have the very same measure. Right here the main angle because that the minor arc actions ???45^circ???, so the young arc is ???45^circ???.


The main angle because that the significant arc is ???315^circ???, for this reason the measure of the major arc is ???315^circ???. The amount of the central angles that a one always include to ???360^circ???.

Naming arcs and their measures

You have the right to name an arc by the letters that surname the beginning and also endpoints that the arc on the circle. For instance the yellow arc shown listed below is arc ???AB???. Rather of writing the word arc, we could additionally use a bent symbol over the letter to suggest the arc, prefer ??? ext arc AB???.


The measure up of arc ???AB??? is offered by the variety of degrees in arc ???AB???. Then you include the symbol ???m??? or the word “measure.” In this instance we have the right to say the measure up of arc ???AB??? is same to ???45^circ???. If we provided all symbols we can write ???m ext arc AB=45^circ???.

How to uncover arc size of part of a circle, based on the measure of the main angle

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Finding the difference in between arc lengths


If???overlineAD??? is a diameter that the circle (with center at ???C???) in the figure, what is the difference in between the steps of???oversetfrownDB??? and arc ???oversetfrownAE????

Note: A diameter is any line segment that passes v the facility of a circle and has both of its endpoints top top the circle. An alert that the diameter is same to double the radius, and also that the diameter splits a circle into two semicircles. In this problem,???overlineAD??? is a diameter the splits the circle into semicircles???AD??? and also ???DA???.

???overlineAD???is a diameter of the circle, which method that the amount of the steps of arc???DB??? and arc???BA??? is ???180^circ???.




Likewise, the amount of the procedures of???oversetfrownAE??? and???oversetfrownED??? is ???180^circ???.




The difference between the actions of arcs???oversetfrownDB??? and???oversetfrownAE??? is

???140^circ -50^circ =90^circ???

Let’s look in ~ one much more example.

You can name an arc by the letters that surname the beginning and endpoints that the arc on the circle.


What is the measure of arc ???MN???, offered that ???overlineLO??? is a diameter of one ???Q????

We have to solve for ???x??? and also then plug it earlier into the expression for the value of arc ???MN???. We recognize that ???overlineLO???is a diameter of circle ???Q???, therefore the amount of the measures of arc ???LP??? and arc ???PO??? is ???180^circ???.

We have the right to use this information to uncover the value of ???x???.

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???m ext arc LP+m ext arc PO=180^circ???

Central edge ???LQP??? has actually a measure of ???154^circ +3x???, which way that arc ???LP??? additionally has the same measure. Then we have the right to say

???154^circ +3x+11^circ +2x=180^circ???

???165^circ +5x=180^circ???



Now us can uncover the measure up of arc ???MN???.

???m ext arc MN=86^circ +2x???

???m ext arc MN=86^circ +2(3^circ)???

???m ext arc MN=92^circ???

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learn mathKrista KingNovember 9, 2020math, find out online, online course, online math, geometry, one geometry, arc, arc of a circle, one arcs, central angle, central angle of an arc, level measure of an arc, minor arcs, major arcs, semi-circular arcs, actions of arcs
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