呢條數點樣計牙??????????急急急急急急急!!!!!!!!!!聽日hand in嫁!!

👨🏻‍🏫 學術台數學

wingyan

2008-04-24 6:05 am

呢條數點樣計牙??????????

-√5/7 + √20

等於咩牙???

列曬d steps牙please!!!

thz!

回答 (2)

用戶82723

2008-04-24 9:17 pm

✔ 最佳答案

-√5/7 +√20
= 2√5 - √5/7
= (2 - 1/7)√5
= 13√5 / 7

答案只係得一個
(其實好正常，你有沒有試過計加減數出現兩個不同的答案?)
因為 √(a^2) = a 唔等於 -a
√ 呢個符號表示「正」平方根
- √(a^2) 先等於 -a

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[匿名]

2008-04-24 9:13 am

-√5/7 + √20

= -√5/7 + √4 * √5

because:

√4 = +/- 2

therefore:

= √5 (-7 + 2) or √5(-7 - 2)

= -5 √5 or -9 √5

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