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SAT Math: Calculating Arc Length Using Proportions 3 Views
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Description:
A circle has a radius of 6 and a central angle ∠XYZ that measures . What is the length of the major arc formed by the central angle?
Transcript
- 00:00
Yeah Whoa Okay Trig shmoop ear's A circle has a
- 00:06
radius of six and a central angle of X Y
- 00:09
Z That measures for pie over three radiance What's the
- 00:11
length of the major arc X Z formed by the
- 00:15
central angle All right so we gotta drive Little picture
Full Transcript
- 00:19
here It's gonna look like this I'm here to here's
- 00:22
to forty And then we got to X and line
- 00:24
Zeke And yes how rude it was of this problem
- 00:27
to not come with a drawing Yeah you have to
- 00:29
make one sometimes but that's because we're in America No
- 00:32
more participation trophies for you Start with the angle here
- 00:35
of four pi over three and converted to degrees We
- 00:39
had for pirating ins over three times the hundred degrees
- 00:42
over pi radiance That's how we got to two Forty
- 00:44
They're spinning counterclockwise Okay And this is how big the
- 00:48
central angle in the circle has to be This thing
- 00:51
which is a pretty big to forty big number Imagine
- 00:54
having to run around the circle to get from X
- 00:55
to Z by taking the longer route Well that's the
- 00:58
root of the major ark We need to measure and
- 01:00
to find the distance around a part of the circle
- 01:03
First find the distance around the full circle which is
- 01:05
the What's it called Oh yes Circumference Well the problem
- 01:08
says the radius is six and the circumference is always
- 01:11
two Pi r Right That's just by definition So sir
- 01:14
Come sir Go to buy our equals two high times
- 01:17
six which is twelve Pie Got it Simple That's the
- 01:20
circumference Well given the circumference here we can measure the
- 01:23
art by setting up a proportion We need to measure
- 01:25
the arc length created by two hundred forty degree arc
- 01:28
out of the full circle Three Sixty measure So what
- 01:31
is that Well we got to forty over three Sixty
- 01:33
There equals that arc x z over twelve pie because
- 01:37
that's a circumference right That's the three sixty Think so
- 01:40
reduces down to two thirds equals xy over twelve pie
- 01:43
Or send another way If we divide the numbers out
- 01:45
here we get well the ark XY is just a
- 01:48
pie So the length of the major arc X Z
- 01:51
formed by the central angle is a pirate's answer See
- 01:54
and remember this is a distance of the long way
- 01:57
From ecstasy not the short way which is for pie
- 02:00
They throw that curve ball like you There'd be and
- 02:02
twelve five's The total circumference on a portion of it
- 02:05
into pie is the full angle of a circle and
- 02:07
radiance so they're always going to give you answers here
- 02:10
That might seem logical on the way back part of 00:02:12.53 --> [endTime] your brain but aren't
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SAT Math 2.1 Geometry and Measurement. What is the measure of angle z in terms of x and y?
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