What is the radius of a circle whose equation is x2 + y2 + 8x – 6y + 21 = 0? units

To answer this, use "completing the square."

x2 + y2 + 8x – 6y + 21 = 0 becomes

x^2 + 8x + 16 - 16 + y^2 - 6y + 9 - 9 + 21 = 0

 (x + 4)^2       -16     + (y - 3)^2     + 12 = 0

or   (x + 4)^2      + (y - 3)^2   = 4

Since 4 = r^2, r = 2 units, and the center is at (-4, 3)

this was already solved by me with a different person. if you look it up in the search bar at the top of the page, you will get the answer.

step-by-step explanation:

answer: c, the green line

step-by-step explanation:

there is no black line, eliminate b.

simple interest implies periodic payments, but the red line shows no payments, eliminate d.

simple interest has equal payments. if paid say every day, the graph is about a straight line (actually a stairstep).

the yellow line is not straight, eliminate a.

check: the green line is straight, answer is c.

simple interest with positive interest rate gives a straight line sloping up to the right. green line:

g(t) = $100 + ($200-$100) ÷ (20 years) × (t years)

= $100 + (4%/year) × ($100)(t years)

incidentally, the yellow line curving upward represents continuously compounded interest

y = $100 × 2^(t years / (14 assuming the yellow line hits $200 at 14 years. 2^0 is 1, so y(0) = $100; 2^(14/14) is 2, so y(14) = $200.