Question

4. Find the center and radius of the circle given by this equation: x2 – 8x + y2 + 4y - 16 = 0

Answer 1

Center ( 4 , -2) and r = 6

Explanation:

x² - 8x + y² + 4y - 16 = 0

x² - 8x + y² + 4 y = 16

x²- 2*4x + y² + 2 *2y = 16

(x² - 2*4x + 16 ) - 16 + (y² + 2*2y + 4) -4 = 16

(x - 4)² + (y + 2)² = 16 + 16 + 4

(x - 4)² + (y -[-2])² = 36

(x- 4)² + ( y - [-2] )² = 6²

Compare with (x - h)²+ (y - k)² = r²

Center ( 4 , -2) and r = 6