Question

Using the following equation, find the center and radius of the circle.
x^2 - 4x + y^2 + 8y = -4
Someone please help me?!

Answer 1

@Mertsj Could you help? i would appreciate it

Answer 2

@ranga @Goldenmoon @Gabylovesyou @Philippians413 @agent0smith @hba

Answer 3

@helpme1.2 @Captainskrullz @vorobya @britneyspears @nikato @mahone331 Help me out?

Answer 4

Do u know how to complete the square?

Answer 5

No i dont understand this at all.

Answer 6

The equation of a circle is usually written in the form

(x-h)^2 + (y-k)^2 = r^2

Where h,k is the center and r is the radius

Answer 7

ohh okay

Answer 8

So ur problem is
(x^2-4x+_) +(y^2+8x+_)=-4

Answer 9

Ur goal now is to try to fill in those 2 blanks

Answer 10

okay.

Answer 11

And to fill in the blank U have to complete the square

Lets start with x^2-4x

Answer 12

okay

Answer 13

how would i do that?

Answer 14

So u know how quadratic eqauionnr written in ax^2+bx+c

Answer 15

yeah okay.

Answer 16

When u complete the square, u want to find c. To find c, u divide b by 2 and then square it

Answer 17

alright

Answer 18

@nikato could you please continue?

Answer 19

Ok, so the c in x^2-4x is 4. Remember the c is always positive. And u'll get
(x^2-4x+4)

This is how I got the 4. The b was -4. So -4/2=-2 and (-2)^2 =4

So can u try to find the c for y^2+8y?

Answer 20

wait so the blank in the equation x^2 - 4x is 4?

Answer 21

+4
And now can u try to find the second blank?

Answer 22

is it 8?

Answer 23

No, so what's the b?

Answer 24

b is -4 right?

Answer 25

No, it's 8. y^2+8x and b would be 8

To find c, divide 8 by 2 and then square ur answer

Answer 26

ohh okay

Answer 27

Now what? what is the center and radius?

Answer 28

Wait, so what did u get for c

Answer 29

i got 8

Answer 30

No, it's 16
8/2=4 and 4^2=16

Answer 31

ohh yeah square! Oops

Answer 32

So now u have (x^2-4x+4)+(y^2+8x+16)=-4+4+16

Added 4 and 16 which are ur c. Becuz u added them on ur left side u have to add them to the right also

Answer 33

Factor

(x-2)^2 +(y+5)^2 = 4^2

Answer 34

And if u look back at one of my earlier post, u can see which is ur center and raius

Answer 35

Is the center (2,5)
and the radius 4?

Answer 36

Center is (2,-5) and ur radius is correct

Answer 37

Okay thank you so much!

Answer 38

Yea, no problem