Respuesta :

2. The chord is bisected by the segment from the center, so you have a right triangle with legs 4 and 6. The hypotenuse is the radius of the circle, x.
   x = √(4^2 +6^2) = √(16+36) = √52
   x = 2√13

4. By the rules for secants, the product of the lengths of the parts of the chord is the same in each case.
   3*7 = 2*x
   x = 21/2
   x = 10.5

6. The measure of angle "a" is the average of the two intercepted arcs.
   a = (165° + 55°)/2
   a = 110°
Of course, b is its supplement.
   b = 180° - 110°
   b = 70°

8. Secant rules again. The products of the near and far lengths are the same in each case. When the segment is a tangent, the near and far lengths are the same, so it is the square of the tangent length.
   x² = 4(4+12) = 64
   x = 8

10. This works the same way as problem 2. Here, it looks like you have a triangle with hypotenuse 6 and side length 3. The other side length is
   half-chord = √(6² -3²) = √(36 -9) = √27 = 3√3
   AB = 2*(half-chord) = 2*3√3
   AB = 6√3

12. The equation of a circle of radius r and center (h, k) is
   (x-h)² + (y-k)² = r²
Of course, the "passes through" point must satisfy the equation, so you have
   (x-3)² + (y-0)² = r² = (-2-3)² + (-4-0)² = 25+16
   (x-3)² + y² = 41

14. Same as 12. Radius is 4.
   (x+5)² + (y-2)² = 16

16. Radius 2, center (0, -1).
   x² + (y+1)² = 4

18. The angle bisectors for the axes are the lines
   y = x
   y = -x
Here's a plot.
Ver imagen sqdancefan