最后一题做不出来 , 15 分.周一要交.是大1的~!!!学数学的帮帮忙~!
use proof by contradiction to show that if a,b and c are odd interers then ax^2+bx+c=0 has no solution in the set of rational numbers.
(You may use standard parity results of the form " odd*odd=odd",“even+odd=odd”,etc)
感激！！！！！！！ 
AX后面是什么符号?
要show that b^2-4ac is not a perfect square，具体怎么证我还在想 
做出来了，就是assume那个rational
然后let a=2t+1 b=2s+1 c=2k+1 然后知道b^2-4ac=一个odd的平方，设一下2m+1
然后两边展开，发现odd=odd-odd，contradiction，应该就是这样
bonbon1983于2008-12-06写道:
use proof by contradiction to show that if a,b and c are odd interers then ax^2+bx+c=0 has no solution in the set of rational numbers.
(You may use standard parity results of the form " odd*odd=odd",“even+odd=odd”,etc)
感激！！！！！！！
take it easy
if x is odd, then odd^3+odd^2+odd=odd+odd+odd=odd
if x is even, then odd*even^2+odd*even+odd=even+even+odd=odd
0 is not odd, so no solution for x
ukinfo于2008-12-06写道:
bonbon1983于2008-12-06写道:
use proof by contradiction to show that if a,b and c are odd interers then ax^2+bx+c=0 has no solution in the set of rational numbers.
(You may use standard parity results of the form " oddodd=odd",“even+odd=odd”,etc)
感激！！！！！！！
take it easy
if x is odd, then odd^3+odd^2+odd=odd+odd+odd=odd
if x is even, then oddeven^2+odd*even+odd=even+even+odd=odd
0 is not odd, so no solution for x
:polite:
MM这个是哪门阿？
我也是学PURE MATHS~
这个题目还OK，不是很难的。以前在中国学过的 :cn15:
用上面俩答案都OK的~~ 
juan_wu于2008-12-06写道:
ukinfo于2008-12-06写道:
bonbon1983于2008-12-06写道:
use proof by contradiction to show that if a,b and c are odd interers then ax^2+bx+c=0 has no solution in the set of rational numbers.
(You may use standard parity results of the form " oddodd=odd",“even+odd=odd”,etc)
感激！！！！！！！
take it easy
if x is odd, then odd^3+odd^2+odd=odd+odd+odd=odd
if x is even, then oddeven^2+odd*even+odd=even+even+odd=odd
0 is not odd, so no solution for x
MM这个是哪门阿？
我也是学PURE MATHS~
这个题目还OK，不是很难的。以前在中国学过的
我猜是大一analysis那种刚开始的题目吧，就是训练逻辑思维 :cn08:
大家都很強!
米人感谢么？？ `` 
世风日下了