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Mathematics 9 Online
zarkam21:

3.742?

zarkam21:

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zarkam21:

@Vocaloid

Vocaloid:

yeah good

zarkam21:

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Vocaloid:

|dw:1517592400909:dw|

Vocaloid:

the center is (-3,2), so h = -3 and k = 2 while the radius is 1 use the picture to write the appropriate equation

Vocaloid:

|dw:1517593193514:dw| simplify, and be careful with parentheses

zarkam21:

A

zarkam21:

wait nvm

zarkam21:

its either c or d

Vocaloid:

(x-h)^2 = (x-(-3))^2 = (x+3)^2 (y-k)^2 = (y-2)^2

zarkam21:

D

Vocaloid:

excellent

zarkam21:

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zarkam21:

point?

Vocaloid:

yeah good (had to look this one up tbh)

zarkam21:

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Vocaloid:

this is what we call "completing the square" in math first we gather up the x terms x^2 - 4x then we take the b -term, divide it by 2, square it, then add it to both sides of the equation x^2 - 4x + 2 + {the y terms but they're not important right now} = 10 + 2 then we factor x^2 - 4x + 2 = (x-2)^2 making h = 3

Vocaloid:

h = 2 sorry sorry

zarkam21:

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zarkam21:

B

Vocaloid:

close but not quite the term on the right hand side needs to be r^2 not just r

zarkam21:

SO D

Vocaloid:

good

zarkam21:

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zarkam21:

-4.5

Vocaloid:

i'm not sure that's right y^2 + by + c = (y+2)^2 (this is taken from the circle equation), c is just some constant that's not important to solving the problem so y^2 + by + c = y^2 + 4y + 4 meaning b = 4

zarkam21:

ooh i see what you did there

zarkam21:

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Vocaloid:

a is just a normal circle w/radius 1 b is not a circle, it's a line c is not a circle (at least not in the real plane, it exists in the imaginary plane only) so d, since this is a point

zarkam21:

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zarkam21:

3.742

Vocaloid:

good

zarkam21:

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Vocaloid:

crap lemme just teach myself this again real quick

zarkam21:

OKay

Vocaloid:

|dw:1517595560710:dw|

Vocaloid:

first find the midpoint of the two vertices, that will give you the center

zarkam21:

midpoint is (2,2)

Vocaloid:

good, and each foci is 3 units away from the center so c = 3 the two vertices are the endpoints of the major axis, so the major axis is 14 units long, making a = 14/2 = 7 c^2 = a^2 - b^2 3^2 = 7^2 - b^2 making b^2 = 40 putting this all together:

Vocaloid:

|dw:1517595896618:dw|

Vocaloid:

so D

zarkam21:

A?

zarkam21:

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zarkam21:

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Vocaloid:

yup A good

zarkam21:

D?

zarkam21:

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Vocaloid:

good, D

zarkam21:

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Vocaloid:

what did you get as your c-value?

zarkam21:

I actually used mathway :o

Vocaloid:

c^2 = b^2 - a^2 c = ?

zarkam21:

\[\sqrt{(b+a)(b-a)}\]

Vocaloid:

using the values from the problem

Vocaloid:

|dw:1517596872313:dw| this is the equation for an ellipse, identify what your a^2 and b^2 would be based on the problem

zarkam21:

okay and then do a^2-b^2

Vocaloid:

yes

zarkam21:

-1392

Vocaloid:

|dw:1517596993589:dw|

Vocaloid:

|dw:1517596998618:dw|

Vocaloid:

so a^2 = 64 b^2 = 52 c^2 = a^2 - b^2 what does c equal?

zarkam21:

37.31

Vocaloid:

c^2 = 64 - 52 c = ?

zarkam21:

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Vocaloid:

good, so c = 2sqrt(3) eccentricity = c/a = ?

zarkam21:

c

Vocaloid:

good

zarkam21:

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zarkam21:

C?

Vocaloid:

good

zarkam21:

A?

zarkam21:

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Vocaloid:

A) is actually just a normal ellipse I believe it's actually C since a degenerate ellipse is a point

zarkam21:

A?

zarkam21:

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Vocaloid:

y needs to be the major axis so the bigger number needs to be below y so C

zarkam21:

D?

zarkam21:

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Vocaloid:

good (I'm working w/ a lot of people rn so you can tag me if I forget about you ;_;)

zarkam21:

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zarkam21:

B?

zarkam21:

@Vocaloid

Vocaloid:

the focal radii is c not a, so 2c

zarkam21:

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zarkam21:

@Vocaloid

zarkam21:

@Vocaloid

Vocaloid:

if we do a quick sketch, we can see that the foci + vertices line up on the y-axis the midpoint is (0,0) using the midpoint of the two vertices meaning the vertices are 4 units apart from the midpoint so the a term is 4 meaning the y^2 term has to have 4^2 = 16 below it making B the only possibility

Vocaloid:

also this q is getting laggy can we open a new one

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