Now we can introduce the really important idea that radians. And I’ll start by saying, have you ever before wondered why a best angle is defined as 90 degrees? Why the number 90? whereby did the idea of levels come from? The mechanism goes back to the old Babylonian religion, over 3000 years ago.

So here’s a photo of the Babylonian God, Marduk, and his pets dragon. These old Babylonians thought that 60 and 360 were spiritual numbers. They thought all kinds of things, they thought a host of strange Gods, castle sacrificed barnyard animals for assorted things. It’s a very old religion that died out a long time ago. But we still cave on come these two numbers.

Turns the end that the Babylonians believed all-the-way roughly a circle should divided into 360 parts, therefore that’s the origin of the degree system. These Babylonian values are likewise the reason we have 60 minutes in one hour and 60 seconds in a minute. So it transforms out that also though this religion has been dead for millennium, turns out your values room still influencing a lot about how us look in ~ the world.

You are watching: Convert 270 degrees to radians in terms of pi Image by kabzarchyk

What is the most basic length linked with the circle, native which everything about the circle could be calculated? clearly the radius. We have the right to calculate the area from the radius, we can calculate the circumference from the radius. We can calculate every little thing we need from the radius.

If we can use the radius the a circle to specify an angular measurement, this can be the communication of a brand-new system for measuring angles. And also this is specifically what we’re gonna do. This system is known as radians. So remember that arcs that circles have length. Expect we made an arc the had exactly the same length as the radius.

So here, we have a little sector. And also of food there room two radiuses going out from the facility of the circle. And also then the arc size also, even though it’s curved, it has actually the exact same length. Therefore all 3 sides of this tiny sector have the same length. This would specify an edge of one radian. And we might use this together a unit that angle.

So we could measure radians around the circle, and also that would be the same thing as measuring the number of radiuses approximately the circle. In fact, we already measure all the way around the circle utilizing radius lengths. We understand that the circumference equates to 2 pi r. And also so that means there are 2 pi radius lengths about the circumference. 2 pi radius lengths every the method around the circle.

This means that there are 2 pi radians every the way around the circle. So all the method around the circle, the point that we offered to contact 360 degrees, we’re currently gonna speak to that 2 pi radians. For this reason if 360 level = 2 pi radians, notification that for degrees we have to use the degree symbol. Radians room so unique that us don’t require a distinct symbol for them.

We don’t need to write r, or radians, or anything choose that. We can just write 2 pi and that indicates that it is 2 pi radians. And also this permits us to number out just how to said the entire level system come the whole radian system. So divide that equation through 2, we acquire 180 = pi, that’s really important. 180 degree angle is the same as a pi radian angle.

Divide that again, a ideal angle i m sorry we use to recognize as 90 degrees, we deserve to now call that an angle of pi/2. So the is the measure up over appropriate angle in radians, pi/2. Currently start v that right angle, if we divide that through 2, then we acquire a 45 degree angle and also that’s pi/4. Again go earlier to the pi/2, rather divide it by 3.

We acquire 30 degrees = pi/6, if us multiply both political parties by 2, we acquire 60 degrees = pi/3. These are the worths of every the one-of-a-kind triangles angle in radians. Therefore the two special triangles one of them is a pi/4, pi/4, pi/2 triangle. The various other is a pi/6, pi/3, pi/2 triangle. The equation, 180 levels = pi is regularly a an excellent place to start since 180 has so plenty of factors.

Suppose we required to find, say, 20 degrees in radians. Well of course, 180 = 20 x 9, and also of food that equates to pi. Just divide both sides by 9 and we get 20 degrees = pi/9. This deserve to be a an extremely quick way if the variety of degrees is an obvious factor of 180. We deserve to also readjust the equation 180 levels = pi into a fraction equal to 1.

So 1 = pi/180, we have the right to multiply any type of degree measure by this fraction to readjust from levels to radians. For example, 270 degrees multiplied by pi/180, we obtain 270 pi/180, i beg your pardon is 27/18. Division top and bottom by 9, we obtain 3 pi/2, for this reason 3 pi/2 is 270 degrees.

In fact, we can define the 4 quadrants in state or radians. The very first quadrant is 0 come pi /2, 0 come a best angle. The 2nd quadrant is pi/2 come pi. A best angle come a complete semicricle. Third quadrant is pi to 3pi/2. The very first quadrant is 3pi/2 to 2pi.

## Identifying

This is often how the test will certainly specify a certain quadrant. They won’t say third quadrant, they will certainly say theta is between pi and 3pi/2. Which of the adhering to is the value of 240 degrees in radians? pause the video and climate we’ll talk around this.

### Method One

Okay, so an approach one, this is a much more visual method. An alert that 240 levels is twice of 120 degrees, and 120 degrees is a 3rd of the circle.

This way that 240 degrees is 2/3 that the circle. A entirety circle is 2 pi, for this reason 2/3 the 2 pi would be 4/3 pi. So that’s what 240 degrees is in radians. That’s technique one.

### Method Two

Method two would it is in the much more methodical method to take that number and multiply by pi/180.

When we multiply, we cancel the 0’s, then we cancel a aspect of 6, and also we obtain 4 pi/3. And so it transforms out the the price is answer selection D. Let me just point out, it’s an extremely methodical to just multiply through pi/180. I’m going to discourage friend from making her 100% of the time go to method for convert to radians.

It’s much much more efficient come think in terms of proportions, and to think visually around the problem. Girlfriend will know radians much more deeply if you’re not simply reliant on multiply by that proportion every time. The radian worths of pi are simple to relate come a visual understanding. A 3pi/4 edge is 3/4 the pi, that way it’s 3/4 the a semicircle.

So it’s really easy come imagine. Take a semicircle, division it into quarters, 3 that those quarters is a 3 pi/4 angle. To know radians deeply as soon as you can think about them visually and numerically. The full benefits of radians are not necessarily obvious at this level.

They come to be far much more evident in calculus, once we begin doing calculus through trigonometric functions. That’s wherein radians really prove their full value. Obviously, the puts us well beyond anything top top the ACT, so we’re not gonna need to worry about that for the ACT. That’s simply a preview because that why radians room so important.

## Summary

In summary, degrees are the common method to measure up angles, however radians are a mathematically preferable method to perform so. The variety of radians in the central angle the the circle equates to the variety of radius-lengths in the arc. This means that 360 degrees all the means around the circle is 2 pi radians and also a 180 degrees, a semicircle, is pi radians.

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To readjust from degrees to radians, we deserve to think about basic proportions, or we deserve to just multiply the number of degrees by the portion pi/180.