f3 laws of indices thx:D

[匿名]

2011-10-10 1:42 am

請告訴我steps是甚麽~我不明白這些題目~謝謝~ :-D

12. (-9 a b^-2 )^-1 a
/ ( ) ^3
(3 a^-1 b)^2 b^-2

Ans: 1
81 a^2 b^6

其實我自己計不到=a^2,但能計到 -81 和b^6

13. It is known that 1 centimeter =10^-2 m, 1 nano-meter = 10^-9 m, 1 kilometer = 10^3 m. Express 0.80 km as nano-meter in scientific notation.

Ans: 8.0 x 10^11 nano-meter

我是將0.8 x 10^3 x 10^-9,但答案不對

14 (b). find x.

91
x^-3 -1 = 125 Ans: 5/6

我計到 x^-3 = 1.728後就不懂了~

(c). find x.

1
( ) ^3x-1 = 8^ 2x+4 Ans: -5/6
4

我計到x=-3.5!! :(

若你知道怎樣計的話,請幫忙!感激不盡~ :->

回答 (1)

CHUN

2011-10-10 2:43 am

✔ 最佳答案

12.左手邊簡化左= a
-81
右手邊係= a^3
b^-6
成條就係= a X b^-6
-81 a^3
最後就會得到= 1
-81 a^2 b^6
13. 1cm=1米x10^-2(佢出黎混淆你)
1nm=1米x10^-9
1米=1km x 10^-3
1nm=1km x 10^-9 x 10^-3=1x10^-12
姐係話1km=1nm x 10^-12
0.8km=0.8 x 10^-12=8.0 x 10^11

14b.通常見到呢D分數,唔洗張佢變成小數
x^-3=216/125
x^3 =125/216
再用計數機,
125=5^3
216=6^3
x^3=5^3 / 6^3
所以x=5/6

14c.(1/4)^3x-1 =8^2x+4
(2^-2)^3x-1=(2^3)^2x=4
(2)^2-6x = (2)^6x+12
所以 2-6x =6x+12
-6x-6x=12-2
-12x = 10
x = 10/-12
x = -5/6

參考: 做呢D數最重要係睇清楚正負,次方加減,乘數...

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