Suppose a circle with center (1, −3) passes through point (1, −1). Which equation represents the circle?

It is C)  (x − 1)^2 + (y + 3)^2 = 4

Step-by-step explanation:

The radius is the distance between the center and the point on the circle.

Center: (1, −3); Point: (1, −1)

Distance formula: d =  square root of {(x2 - x1)^2 + (y2 - y1)^2}

r = square root of  {(1 − 1)^2 + (−1 + 3)^2 }

r =  square root of {0 + 4 } = 2

(x − h)^2 + (y − k)^2 = r2 > (x − 1)^2 + (y + 3)^2 = 4

Hope this isn't confusing and helps. I also know its right because I just did this on USA Testprep.

hello from mrbilldoesmath!

answer:

25x^2 + 90x + 84

discussion:

mn(x) = m(n(x)) = m( 5x + 9) =

(5x + 9)^2 + 3 =>

25x^2 + 90x + 9^2 + 3 =

25x^2 + 90x + 84                 (as 9^2 = 9*9 = 81)

which is the second choice

regards,  

mrb

p.s.   i'll be on vacation from friday, dec 22 to jan 2, 2019. have a great new year!