我記得 herman yeung 都係用呢個方法
我係用另一個方法
不過都係大同小異
[DSE數學2018] Maths 討論區 (2)
dse杏林
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設 I 為 CE 的延線與 DA 的延線的交點
然後用 AFH ~ CBH 同埋 IFG ~ CBG 呢兩對相似三角形求 BG : GH : HF
然後用 AFH ~ CBH 同埋 IFG ~ CBG 呢兩對相似三角形求 BG : GH : HF
個人認為通常都用處不大
剛才用 geogebra 畫嘅時候發現咗一樣嘢
就係 E H D 三點似乎係共線
就係 E H D 三點似乎係共線
Area of traingle ABC = 60
Since AB = 2EB,
So the area of ACE = 30
Area of HCG = 1/2*CH*CG*sin(x)
Area of ACG = 1/2*AC*EC*sin(x)
Area of HCG : Area ACE = (CH/AC)*(CG/EC)
Area of ACG = 30
=> Area of HCG = 30*(CH/AC)*(CG/EC) .........(i)
Extend BF and CD such that they meet at K
=> CD = DK
Consider the triangle CHK and AHB
AH/CH = 1/2
=> CH/AC = 2/3 .............(ii)
Consider the triangle BGE and KGC
EG/GC = 1/4
=> CG/EC = 4/5..... (iii)
From (i), (ii) and (iii)
Area of HCG = 16
=> Area of AHGE = 30 -16 =14
Since AB = 2EB,
So the area of ACE = 30
Area of HCG = 1/2*CH*CG*sin(x)
Area of ACG = 1/2*AC*EC*sin(x)
Area of HCG : Area ACE = (CH/AC)*(CG/EC)
Area of ACG = 30
=> Area of HCG = 30*(CH/AC)*(CG/EC) .........(i)
Extend BF and CD such that they meet at K
=> CD = DK
Consider the triangle CHK and AHB
AH/CH = 1/2
=> CH/AC = 2/3 .............(ii)
Consider the triangle BGE and KGC
EG/GC = 1/4
=> CG/EC = 4/5..... (iii)
From (i), (ii) and (iii)
Area of HCG = 16
=> Area of AHGE = 30 -16 =14
A=0, b=B, d=D, C=b+d, E=b/2, F=d/2, dxb=120
BF=d/2 + t(-d/2+b), CE=b/2 + s(b/2+d)
solving, G=d/5+3b/5, H=b/3+d/3
area = (B-H)x(-H)/2 - (B-G)x(E-G)/2
=(2b/3-d/3)x(-b/3-d/3)/2 - (2b/5-d/5)x(-b/10-d/5)/2
=120/9+120/18-120/25-120/100
=20-6=14
vector 爆到, coordinate都應該差唔多
BF=d/2 + t(-d/2+b), CE=b/2 + s(b/2+d)
solving, G=d/5+3b/5, H=b/3+d/3
area = (B-H)x(-H)/2 - (B-G)x(E-G)/2
=(2b/3-d/3)x(-b/3-d/3)/2 - (2b/5-d/5)x(-b/10-d/5)/2
=120/9+120/18-120/25-120/100
=20-6=14
vector 爆到, coordinate都應該差唔多
Core Mc 做完無時間check卷係咪正路
絕對唔正路
起碼要全由頭到尾check四次
可唔可以拍片示範下
可以點示範
最尾派咗出嚟個分會證明一切
最尾派咗出嚟個分會證明一切
就算你拎到45題全部啱晒
都證明唔到你夠時間由頭到尾check四次喎
都證明唔到你夠時間由頭到尾check四次喎
所以證唔到
信不信由你
信不信由你
假設 r 為圓半徑
angle at circumference 為 90 度時 chord 幾長？
angle at circumference 為 180 度時 chord 幾長？
兩個情況下嘅 chord 相差幾多倍？
angle at circumference 為 90 度時 chord 幾長？
angle at circumference 為 180 度時 chord 幾長？
兩個情況下嘅 chord 相差幾多倍？
一定係兩倍
think about angle at centre twice angle at circumference