暑期作業既ＭＡＴＨＳ

頭兩題難，請記著："蘋果加蘋果，橙加橙"這原則。

1. a+2b+3c+4a-6b-2c
= a+4a + 2b-6b + 3c-2c
= 5a - 4b +c

2. 2xy+3x-2y+4x-6y+5xy
= 2xy+5xy +3x+4x -2y-6y
=7xy +7x -8y

第三題也難，請記著一架以變速度移動的車，有公式：
移動路程=速度 x移動時間

3. (a) Distance travelled by the car in t second = v (metre per second) x t (seconds)
= vt (metres)
(b) Distance travelled by the car at a speed of 210 metre per second in 1.5 minutes
= 210 metres per second x 1.5 minutes
= 210 metres per second x (1.5 x 60) seconds
= 18,900 metres
=18.9 km

(註：題3(b) 的車子的時速為 210 x 60 x 60 (metres per hour) = 756 km per hour. 太快了吧！)

第四題則不清楚所謂 "do the following questions"，試試吧！

4.(a) 2x(3x-4) = (2x)(3x) - (2x)(4) [乘法分配性質：a(b-c) = ab - ac]
= 6 (x^2) -8x

(b) (9-m) (4m) = (9)(4m) - (m)(4m) [乘法分配性質：(a-b)c = ac - bc]
= 36m - 4(m^2)

希望幫到你！

1. a+2b+3c+4a-6b-2c
=5a-4b+c

2. 2xy+3x-2y+4x-6y+5xy
=7xy+7x-8y

3. (a) distance= vt m
(b) distance = 210 x 60 x 1.5 = 18900 m

4. (a) 2x(3x-4) = 6x^2 - 8x
(b) (9-m)(4m) = 36m - 4m^2