3 CÁCH CHỨNG MINH TIẾP TUYẾN CỦA ĐƯỜNG TRÒN HAY SỬ DỤNG. ÔN THI TOÁN 9 - LUYỆN THI VÀO 10

3 WAYS TO PROVE THE TANGENT OF A CIRCLE OFTEN USED. MATH REVIEW FOR GRADE 9 - GRADE 10 ENTRANCE EXAM ► REGISTER FOR OFFLINE STUDY: MR. CUONG - 09.76.79.85.58 - HUNG SON - DAI TU - THAI NGUYEN ► MR. CUONG'S MATH GROUP:   / loptoanthaycuong   ► Fanpage:   / hoctoanthaycuong   ► DON'T FORGET TO LIKE, SHARE AND SUBSCRIBE TO SUPPORT MR. https://goo.gl/bRVa2w ► SEE MORE LESSONS ON BLOG: http://hoctoancap2.com Fanpage: ► COMMENT YOUR OPINIONS BELOW THE VIDEO, THANK YOU! (❤‿❤) CONNECT ★ Youtube channel: https://goo.gl/zXAQXo ★ SUBSCRIBE: https://goo.gl/bRVa2w ★ Google+: https://goo.gl/LZ8g3y Problems proving the tangency of a circle in polar geometry grade 9. Problems proving the tangency of a circle is a basic but quite good type of problem in the circle chapter of geometry grade 9. This type of problem is also very common in exam questions, so today I would like to send you some good selected problems on proving that a line is a tangent to a circle How to prove that a line is a tangent to a circle Usually there are 2 ways to prove: Method 1: Prove that the line and the circle have only one common point. Method 2: Prove that the line is perpendicular to the radius of the circle at a point on the circle. This point is called the point of contact. Selected tangent problems or Problem 1: Given circle (O;R) with diameter BC, take point A on (O) so that AB=R a. Prove that triangle ABC is a right triangle and calculate the length of BC according to R. b. The tangent at A of (O) intersects line BC at M. On (O), take point D so that MD=MA (D is different from A). Prove that MD is tangent to (O). Problem 2: Given equilateral triangle ABC inscribed in circle (O), AB=43–√. Diameter AD intersects BC at H. Line BO intersects tangent at A of circle (O) at point E. a. Prove that AH is perpendicular to BC, calculate the length of AH and the radius of circle (O). b. Prove that EC is tangent to (O) and quadrilateral ABCE is a rhombus Problem 3 Given semicircle with center O and diameter AB=2R. On the semicircle, take point C (C is different from A and B). Let D be the intersection of line BC with the tangent at A of the semicircle with center O and I is the midpoint of AD. a. Prove that BC.BD=4R2 b. Prove that IC is tangent to the semicircle with center O