Test 1 Sec4 #24 help!
For this one, you’re looking for the equation of a circle with a center of that passes through . The best way to go here is just to build the equation.
For this test, you should know the standard circle equation: A circle with center and radius r has the equation . You can fill in the left side immediately: The center of this circle is (0, 4), so the left side should be .
To fill in the right side, you need to find (or ). Easy enough:
So the answer you want is A.
A note for those who like quick and dirty solutions: Once you’ve got the left side of the equation, you know the answer must be either A or C. If you’re paying close attention, you’ll notice that the only difference between A and C is on the right side of the equation: A says and C says . If you’re in a hurry, that’s probably good enough—you know you’re looking for a squared value, and A provides it.
Another note: if you can’t remember the circle equation, you can still get this question right! Use your calculator to plug and into each answer choice. Only one will work. 🙂