tailieunhanh - Sat - MC Grawhill part 42

Tham khảo tài liệu 'sat - mc grawhill part 42', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 400 McGRAW-HILL S SAT Lesson 8 Circles Circle Basics Okay we all know a circle when we see one but it often helps to know the mathematical definition of a circle. A tangent is a line that touches or intersects the circle at only one point. Think of a plate balancing on its side on a table the table is like a tangent line to the plate. A tangent line is always perpendicular to the radius drawn to the point of tangency. Just think of a bicycle tire the circle on the road the tangent notice that the center of the wheel must be directly above where the tire touches the road so the radius and tangent must be perpendicular. A circle is all of the points in a plane that are a certain distance r from the center. The radius is the distance from the center to any point on the circle. Radius means ray in Latin a radius comes from the center of the circle like a ray of light from the sun. The diameter is twice the radius d 2r. Dia- means through in Latin so the diameter is a segment that goes all the way through the circle. The Circumference and Area It s easy to confuse the circumference formula with the area formula because both formulas contain the same symbols arranged differently circumference 2nr and area nr2. There are two simple ways to avoid that mistake Remember that the formulas for circumference and area are given in the reference information at the beginning of every math section. Remember that area is always measured in square units so the area formula is the one with the square area nr2. Example In the diagram above point M is 7 units away from the center of circle P. If line l is tangent to the circle and MR 5 what is the area of the circle First connect the dots. Draw MP and PR to make a triangle. Since PR is a radius and MR is a tangent they are perpendicular. Since you know two sides of a right triangle you can use the Pythagorean theorem to find the third side 52 PR 2 72 Simplify 25 PR 2 49 Subtract 25 PR 2 24 PR 2 is the radius squared. Since the area of .