「數學」- 圖形面積及周界

1) 平行四邊形面積
= 5 x 9
= 45 (cm^2)
三角形面積
= (12-5) x 9 x 1/2
= 31.5 (cm^2)
總面積
= 45 + 31.5
= 76.5 (cm^2)

2) 圓面積
= 21^2 x 3.14
= 1384.74 (cm^2)
正方形面積
= 30^2
= 900 (cm^2)
陰影面積
= 1384.74 - 900
= 484.74 (cm^2)

3) Sorry the link is dead. I can't see the pic.

2008-05-20 11:15:21 補充：
3) Draw a line AC
Area triangle ADC
= 20 x 20 x 1/2
= 200 (cm^2)
Area of arc ADC
= 20^2 x 3.14 x 1/4
= 314 (cm^2)

Area of shaped area
= 2(area of arc ADC - area of triangle ADC)
= 2(314-200)
= 228 (cm^2)

1.9x5+9x(12-5)除2
=45+9x7除2
=45+31.5
=76.5units

2.咩R??

3.20x20-20除2