F.3 MATHS

A regular square based pyramid is a polyhedron with 8 equal edges.How mang planes of reflection does the solid have?
一個四方金字塔(square based pyramid)共有5個面。

If the speed of a car is decreased by 40%,find the percentage change in the time taken for the car to travel the same journey.
設速率為 v，距離為 s，所而的時間為 t
則
s = v t
若 s 不變，v = (1 – 40%)vo
則
s = v t = vo to
(1 – 40%)vo t = vo to
0.6 vo t = vo to
t = 1.667to
t 增加了 t – to = 0.667to = 66.7%to
即增加了 66.7%
Given the coordinates of P are (-1,2).If Q is the image of P after rotating 90* clockwise about the origin, find the distance between PQ.

圖片參考：http://hk.geocities.com/namsm4e/P0310.jpg

如圖 Q 的坐標為(2, 1)
所以 PQ相距
d = √[(2 – (-1))2 + (1 – 2)2]
= √10

s = v t
v = (1 – 40%)vo
s = v t = vo to
(1 – 40%)vo t = vo to
0.6 vo t = vo to
t = 1.667




Q(2, 1)
d = √[(2 – (-1))^2 + (1 – 2)^2]
= √10