maths23－dlxpxv7的部落格

標題:

maths23

發問:

http://i270.photobucket.com/albums/jj88/ucc041087/23.jpg plz help me to ask above website Qs，thz

最佳解答:

a. Since AB and BD are the tangents to the smaller circle So, AB = BD (tangent property) Since BC and BD are the tangents to the larger circle So, BC = BD (tangent property) So, AB = BC b. ΔABDand ΔBCD are isoscelesΔs. Let ∠BAD= ∠ADB = x ∠BCD= ∠BDC = y ∠ABD= 180? - ∠ABD- ∠ADB = 180? - 2x (∠ sum of Δ) At the same time, ∠BCD +∠BDC = ∠ABD (ext. ∠ of Δ) 2y = 180? - 2x x + y = 90? ∠ADC = ∠ADB +∠BDC = x + y = 90?