Tham khảo tài liệu 'sat math essentials_6', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | GEOMETRY REVIEW There are two rules related to tangents 1. A radius whose endpoint is on the tangent is always perpendicular to the tangent line. 2. Any point outside a circle can extend exactly two tangent lines to the circle. The distances from the origin of the tangents to the points where the tangents intersect with the circle are equal. Practice Question What is the length of AB in the figure above if BC is the radius of the circle and AB is tangent to the circle a. 3 b. 3V2 c. 6V2 d. 6V3 e. 12 125 --------------------------------- GEOMETRY REVIEW ------------------------------------- Answer d. This problem requires knowledge of several rules of geometry. A tangent intersects with the radius of a circle at 90 . Therefore AABC is a right triangle. Because one angle is 90 and another angle is 30 then the third angle must be 60 . The triangle is therefore a 30-60-90 triangle. In a 30-60-90 triangle the leg opposite the 60 angle is V3 X the leg opposite the 30 angle. In this figure the leg opposite the 30 angle is 6 so AB which is the leg opposite the 60 angle must be 6V3. Polygons A polygon is a closed figure with three or more sides. Example Terms Related to Polygons A regular or equilateral polygon has sides that are all equal an equiangular polygon has angles that are all equal. The triangle below is a regular and equiangular polygon Vertices are corner points of a polygon. The vertices in the six-sided polygon below are A B C D E and F. 126 GEOMETRY REVIEW A diagonal of a polygon is a line segment between two non-adjacent vertices. The diagonals in the polygon below are line segments AC AD AE BD BE BF CE CF and DF. Quadrilaterals A quadrilateral is a four-sided polygon. Any quadrilateral can be divided by a diagonal into two triangles which means the sum of a quadrilateral s angles is 180 180 360 . Sums of Interior and Exterior Angles To find the sum of the interior angles of any polygon use the following formula s 180 x 2 with x being the number of sides in
