20 Days to Go(-5 Days): 三角形之間隱藏的關係

Q1

In the figure, D is a point lying on AC such that BD is perpendicular to AC. It is given that AD = 8 cm and DC = 18 cm . Find the length of BD.

呢種題型係經常都考 , 我地會用90^o– x , x 同90^o去證明兩個三角形Similar

而且因為題目只提供兩條邊 , 所以選擇邊一對Similar Triangle(圖中有3對)係要考慮兩個三角形都同時有BD呢一條邊

Q2

In the figure, O is the center of the circle and AOC is a straight line. If AB and BC are tangents to the circle such that AB = 3 and BC=4, then the radius of the circle is

首先 , 因為圖中出現Circle , 所以一定會用到圓形properties

然後 , 因為題目提供AB同BC係Circle的Tangent , 所以我地會遁Tangent呢一個方向去諗

而問題又係問有關Radius , 所以會聯想到 (Tangent perpendicular to radius)

加兩條線DO , OE (Radius) , 形成兩個細直角三角形

可能同學到呢一個位會無方向

呢個時候就應該諗一諗Similar Triangle

想睇2019年DSE Math LQ同MC既參考答案CLICK呢度啦！

Q3

In the figure, AB and AC are the tangents to the circle at B and C respectively. BD is a diameter of the circle. AC produced and BD produced meet at E. If AB = 6 cm and AE = 10 cm , then BD =