我想問如果係計inequality,
eg. x^2+x+3>0
甘樣,answer應該係no solution 定all real value???
幾時會係no solu 幾時會係all real value????
thz~
AMATH - all real no. and no solution
2007-12-18 2:10 am
回答 (2)
2007-12-18 4:12 am
✔ 最佳答案
I've handwritten 3 pages ar...remember to read carefully la><
it's just like revising that part again...="=
hope that it helps laXD
http://i19.photobucket.com/albums/b163/Pealie/forum%20stuff/Save0001.jpg?t=1197893313
http://i19.photobucket.com/albums/b163/Pealie/forum%20stuff/Save-1.jpg?t=1197893301
http://i19.photobucket.com/albums/b163/Pealie/forum%20stuff/Save0002-1.jpg?t=1197893298
參考: myself...
2007-12-18 2:16 am
我地通常係用配方法去計
x^2+x+3>0
=x^2+x+(1/2)^2-(1/2)^2+3>0
=(x+1/2)^2+11/4>0
=(x+1/2)^2>-11/4
由於對所有實數x,x^2必大於或等於0,所以(x+1/2)^2>-11/4對所有實數x都成立
所以方程既解係所有實數
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如果係x^2<0或一個負數,咁就係no solution
x^2+x+3>0
=x^2+x+(1/2)^2-(1/2)^2+3>0
=(x+1/2)^2+11/4>0
=(x+1/2)^2>-11/4
由於對所有實數x,x^2必大於或等於0,所以(x+1/2)^2>-11/4對所有實數x都成立
所以方程既解係所有實數
----------------------------------------------------------
如果係x^2<0或一個負數,咁就係no solution
收錄日期: 2021-04-25 17:27:27
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