thx:)
更新1:
WHY NEED - 2xy?? @@
maths (f.2) quick~
回答 (2)
2014-01-04 2:27 am
✔ 最佳答案
x + y = 5Squaring both sides, we get
(x + y)^2 = 5^2
x^2 + 2xy + y^2 = 25
But xy = 6
That is x^2 + 2(6) + y^2 = 25
x^2 + 12 + y^2 = 25
So x^2 + y^2 = 25 - 12 = 13.
2014-01-03 9:56 pm
Answer: 13
x^2 + y^2
= (x + y)^2 - 2xy
= (5)^2 - 2(6)
= 13
2014-01-03 15:12:05 補充：
(x + y)^2 = x^2 + 2xy + y^2
(x + y)^2 - 2xy = x^2 + y^2
2014-01-03 15:13:42 補充：
WHY NEED ???
DO YOU MEAN (x + y)^2 = x^2 + y^2 ??? @@@
2014-01-03 15:14:38 補充：
(3 + 4)^2 = 3^2 + 4^2 ??? @@@
7^2 = 9 + 16 ??? @@@
49 = 25 ??? @@@
x^2 + y^2
= (x + y)^2 - 2xy
= (5)^2 - 2(6)
= 13
2014-01-03 15:12:05 補充：
(x + y)^2 = x^2 + 2xy + y^2
(x + y)^2 - 2xy = x^2 + y^2
2014-01-03 15:13:42 補充：
WHY NEED ???
DO YOU MEAN (x + y)^2 = x^2 + y^2 ??? @@@
2014-01-03 15:14:38 補充：
(3 + 4)^2 = 3^2 + 4^2 ??? @@@
7^2 = 9 + 16 ??? @@@
49 = 25 ??? @@@
參考: knowledge
收錄日期: 2021-04-25 22:39:01
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20140103000051KK00065