中三-四邊形20點

1.
x = 3 (平行四邊形對邊)

2y = 5 (平行四邊形對邊)
y = 2.5


2.
2a = 60° (平行四邊形內對角)
a = 30°

3b + 60° = 180° (同側內角和, PQ//SR)
b= 40°


3.
2x = 5 (平行四邊形對角線互相平分)
x = 2.5

x + y = 5 (平行四邊形對角線互相平分)
2.5 + y = 5
y = 2.5


4.
a = 70° (內錯角,RU//ST)

(a + 60°) + b = 180° (同側內角和, UT//RS)
(70° + 60°) + b = 180°
b = 50°


5.
EB = EC
ΔEBC 為一等腰三角形。
∠C = (180° - 50°)/2 = 65°

x = 65° (平行四邊形內對角)

y + 65° = 180° (同側內角和, AD//BC)
y = 115°

1) 平行四邊形對邊相等
x = 3
2y = 5
y = 2.5

2) 平行四邊形對角相等
2a = 60
a = 30

3b+60 = 180 (同旁內角)
3b = 120
b = 40

3) 平行四邊形對角線互相平分
2x = 5
x = 2.5

x+y = 3
2.5+y = 3
y = 0.5

4) 60+70+b = 180 (三角形內角和及平行四邊形對角相等)
b = 50

a+60+50 = 180 (同旁內角)
a = 70

5) EB = EC
角EBC+角ECB+50 = 180 (三角形內角和)
角EBC = 角ECB (等腰三角形底角)
角EBC+角ECB+50 = 180
角EBC+角ECB = 130
角EBC = 角ECB = 65
y+65 = 180 (同旁內角)
y = 115

x+y = 180 (同旁內角)
x+115 = 180
x = 65

1.
x=3
y=5/2
2.
a=60/2=30
3b+2a=180
3b+2‧30=180
3b=120
b=40
3.
x=5/2
x+y=3
5/2+y=3
y=1/2
4.
a=70
b+a+60=180
b+70+60=180
b=50
5.
x+x+50=180
2x=130
x=65
y+x=180
y+65=180
y=115

1. x=3cm , y唔知
2. a=30 , b=40
3. x=2 , y=1
4. a=70 , b=50
5. x=70 , y=110

以上答案未必岩晒
但可以作參考