*Hãy chứng minh theo chiều ngược lại a) Nếu I là trung điểm của đoạn thẳng

AB thì với mọi điểm M ta có :

vectơ MA + vectơ MB = 2 vectơ MI

b) Nếu G là trọng tâm của tam giác

ABC thì với mọi điểm M ta có vectơ MA + vectơ MB + vectơ MC

= 3 vectơ MG

Match the following terms with their definitions. 1. bisector of a segment ray ba and ray bc are opposite rays if a, b, and c are collinear and b (the endpoint of both rays) is between a and c. 2. opposite rays a ray, , is the set of points beginning at point a and going infinitely in the direction of point b. 3. collinear points a line or segment that intersects the segment at its midpoint. 4. betweenness of points a set of two or more points all on the same line. 5. ray the distance between the endpoints of a segment. 6. space point b is between a and c if a, b, and c are collinear and the equation ab + bc = ac is true, where ab, bc, and ac are the distances between points a and b, b and c, and a and c, respectively. 7. midpoint of a segment a set of two or more points all on the same plane. 8. coplanar points the point on a segment that divides the segment into two equal segments. 9. length of a segment the set of all possible points. 10. line segment the set of two different endpoints and all points between them.

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).

What is the greatest number of parts of a circle that can be formed by cutting the circle with 7 straight cuts? (note: the parts do not have to be equal in size)