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Teachers & SchoolsWhat is the radius of a circle with a center at (-4, 5) and a point on the circumference at (2, 13)?

Product Type | SAT Math |

SAT | SAT Math |

SAT Math | Additional Topics in Math Geometry and Measurement |

Test Prep | SAT Math |

from hurting it because math problems don't wear protective headgear

Well here's a standard form circle where H K's a

center Yeah you know this one Well plug in the

centre point for H and K being careful about the

signs Yeah I saw the sign song about that So

we've got X plus four squared Plus Wyman five squared

equals R squared were only given a random point on

this circle And we can put that point to good

use So just plug it in for X and y

It's how easy this is We love circles so we

get two plus four squared plus theta two minus five

squared equals R squared Well six squared plus eight square

It is you thirty six plus sixty fourths Hundreds are

scared So are squared of one hundred which is in

the radius of the circle Just ten Yeah well that

was one way to solve the problem Another way would

be with a distance formula the distance from the centre

to any part of the circle's edge Is the radius

rights basically the definition Well we could have used the

distance formula to measure the distance from the center to

a random spot on the edge by plugging in the

values of the two points that were given like this

So the distance is ah this thing And then we

just plug in the negative four minus two squared plus

five minus thirteen square there And that gets us formula

Looks a whole lot like what we just did only

coming at it from a side view mirror Well either

way works but whichever you choose tackle it gently so 00:01:33.23 --> [endTime] it's Mom doesn't get too worried and that's it