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Mathematics 14 Online
OpenStudy (anonymous):

Please help!! posting pic below!!

OpenStudy (anonymous):

OpenStudy (anonymous):

@Luigi0210

OpenStudy (anonymous):

@Nnesha

OpenStudy (anonymous):

@Michele_Laino can you help me???

OpenStudy (anonymous):

please ive been stuck on this :/

OpenStudy (michele_laino):

hint: as we can see, from the graph, the center of the circle, is: \[\Large C = \left( { - 1.5,1.5} \right)\] so if we consider any generic point \(P=(x,y)\) of the circle, the distance \(PC\), is: \[\Large d\left( {C,P} \right) = \sqrt {{{\left( {x - \left( { - 1.5} \right)} \right)}^2} + {{\left( {y - 1.5} \right)}^2}} \]

OpenStudy (anonymous):

So C?

OpenStudy (michele_laino):

hint: of course, such distance, has to be equal to the radius of the circle, and the radius of the circle is \(r=3/2=...\)

OpenStudy (michele_laino):

that's right!

OpenStudy (anonymous):

Choose the correct standard form of the equation of a circle given the following radius and coordinates. r = 11, (0, 0) Select one: a. x^2 + y^2 = 121 b. (x – 0)^2 + (y – 11)^2 = 0 c. Either A or B d. None of the above

OpenStudy (michele_laino):

I confirm option C

OpenStudy (anonymous):

can you help me with the question i posted above ?

OpenStudy (michele_laino):

since the center is \(C=(0,0)\), and the radius is \(r=11\), then the distance \(d\) of a generic point of the circle from the center, is: \[d\left( {C,P} \right) = \sqrt {{{\left( {x - 0} \right)}^2} + {{\left( {y - 0} \right)}^2}} \] again such distance has to be equal to the radius of the circle

OpenStudy (anonymous):

So theres more than one option? so C?

OpenStudy (michele_laino):

I think that there is only one correct option

OpenStudy (anonymous):

I think B

OpenStudy (michele_laino):

hint: from my replies above, we can write this: \[\sqrt {{{\left( {x - 0} \right)}^2} + {{\left( {y - 0} \right)}^2}} = 11\]

OpenStudy (anonymous):

yeah B

OpenStudy (michele_laino):

hint: if I take the square of both sides of last equation, I get: \[{\left( {x - 0} \right)^2} + {\left( {y - 0} \right)^2} = {\left( {11} \right)^2}\]

OpenStudy (anonymous):

D?

OpenStudy (michele_laino):

I think it is option A, since we can write this: \[\begin{gathered} {\left( {x - 0} \right)^2} + {\left( {y - 0} \right)^2} = {x^2} + {y^2} \hfill \\ {\left( {11} \right)^2} = 121 \hfill \\ \end{gathered} \]

OpenStudy (anonymous):

oh okay

OpenStudy (anonymous):

Choose the correct standard form of the equation of a circle given the following radius and coordinates. r = 4, (–2, 8) Select one: a. x2 + y2 = 4 b. (x – 2)^2 + (y – 8)^2 = 16 c. (x + 2)^2 + (y + 8)^2 = 4 d. (x + 2)^2 + (y – 8)^2 = 16

OpenStudy (michele_laino):

again, we can write this equation for the distance between a generic point \(P=(x,y)\) and the center of the circle \(C=(-2,8)\): \[d\left( {C,P} \right) = \sqrt {{{\left( {x - \left( { - 2} \right)} \right)}^2} + {{\left( {y - 8} \right)}^2}} = 4\]

OpenStudy (michele_laino):

now, please take the square of such equation, namely: \[{\left( {\sqrt {{{\left( {x - \left( { - 2} \right)} \right)}^2} + {{\left( {y - 8} \right)}^2}} } \right)^2} = {4^2}\]

OpenStudy (anonymous):

C?

OpenStudy (michele_laino):

no, I'm sorry, since \(4^2=16\)

OpenStudy (michele_laino):

hint: after a simplification, we get: \[{\left( {x - \left( { - 2} \right)} \right)^2} + {\left( {y - 8} \right)^2} = 16\]

OpenStudy (anonymous):

D or B

OpenStudy (anonymous):

B

OpenStudy (michele_laino):

yes! So, option D or option B?

OpenStudy (anonymous):

B right??

OpenStudy (michele_laino):

no, I'm sorry, option B is wrong, since in my equation we have: \[x - \left( { - 2} \right) = x + 2\]

OpenStudy (anonymous):

oh okay i got my signs messed up

OpenStudy (anonymous):

would you mind?

OpenStudy (anonymous):

if not its ok

OpenStudy (michele_laino):

I think that the point \((1,0)\) is the center, right?

OpenStudy (anonymous):

i believe so

OpenStudy (michele_laino):

so, we can write this equation for the distance between a generic point \(P=(x,y)\) from the center: \[\sqrt {{{\left( {x - 1} \right)}^2} + {{\left( {y - 0} \right)}^2}} = {\left( {\frac{1}{4}} \right)^2}\]

OpenStudy (anonymous):

and that leaves us with either A or C i believe

OpenStudy (michele_laino):

oops.. I have made a typo: \[\sqrt {{{\left( {x - 1} \right)}^2} + {{\left( {y - 0} \right)}^2}} = \frac{1}{4}\]

OpenStudy (michele_laino):

hint: again, if I take the square of both sides of such equation, I can write: \[{\left( {x - 1} \right)^2} + {\left( {y - 0} \right)^2} = {\left( {\frac{1}{4}} \right)^2}\]

OpenStudy (anonymous):

oh no B then

OpenStudy (michele_laino):

yes! that's right!

OpenStudy (anonymous):

thanks so much (:

OpenStudy (michele_laino):

:)

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