MATHS

1)Since the values of x,y and z form an arithematic sequence

Let d be the common difference.
x = (a﹣d) cm , y = a cm , z = (a + d) cm
x + y + z = 42
(a﹣d) + a + (a + d) = 42
3a = 42
a = 14
then by Pyth. theorem, we have x2 + y2 = z2
(a﹣d)2 + a2 = (a + d)2
a2﹣2ad + d2 + a2 = a2 + 2ad + d2
a2﹣4ad = 0
142﹣4(14)d = 0
d = 3.5
Hence, x = (14﹣3.5) cm = 10.5cm
y = 14 cm , z = (14 + 3.5) cm = 17.5 cm
The sides of the triangle are 10.5 cm, 14 cm and 17.5 cm respectively.

2)x,100,y form a geometric sequence,
i.e., T(2) / T(1) = T(3) / T(2)
So 100 / x = y / 100
100(100) = xy
xy = 10000
log x + log y
= log (xy)
= log (10000)
= 4

2008-11-02 19:15:17 補充：
第1題你都可以設a是首項，
x = a , y = a + d , z = a + 2d 去計，
但就要用聯立方程去計。