✔ 最佳答案
1.
In 8 minutes the ball falls -30 m/min x 8 min = -240 m (negative sign indicates the ball is falling)
Since the ball is 400 m above the ground, it has positive value + 400
The height of the ball after 8 minutes = + 400m – 240 m = + 160 m
Positive sign indicates the ball is above ground.
The height of the ball after 8 minutes is + 160 m
2.consider the expression (-1)x(-1)x(-1)x......x(-1).what is th value if the number of -1's is odd? What if the number of -1's is even?Explain your answer briefly. thx a lot!!
(-1)^odd number = -1
(-1)^even number = +1
the value = -1 if the number of -1's is odd
(-1)x (-1) = +1
(-1)x (-1) = +1
(-1)x (-1) = +1
,,,,,,,,,,,,,,,
A pair consists of two (-1)
For a pair (-1)x(-1) = +1
For n pairs , there are 2n number of (-1) = (+1) ^n = +1
When n pairs is multiplied by one (-1), there are odd number (-1),
When the number of (-1) is odd, the product = value of n pairs x (-1) = (+1)(-1) = -1
2012-08-07 07:50:32 補充：
the value = -1 if the number of -1's is odd (Answer)
Qustion 2. 補答
the value = +1 if the number of -1's is even (Answer)
