math test revision

2014-11-03 8:26 am
1 (a)show that the graph of quadratic function y=-mx^2+(2m+n)x+2n cuts the x axis at 2 distinct points if m and n have the same sign.

(b)suppose alpha and beter are the roots of the quadratic equation as the same as that in (a). if the sum of the cube of the roots is 10n/m+5n^2/m^2,show that (m+n)(2m+n)(4m+n)=0.0

omg and who can teach me the techniques of doing such questions?i always cannot look through the tricky points in the questions and it really upsets me! it seems like i cannot improve even if i did a lot exercises! i am frustrated ! should i give up?������������

回答 (3)

2014-11-03 9:34 am
✔ 最佳答案
Please Read:


圖片參考:https://s.yimg.com/rk/HA07344914/o/86598585.png


2014-11-03 01:46:56 補充:
For 1a)
Since y=-mx²+(2m+n)x+2n cuts the x axis at 2 distinct points
you needs to prove Δ>0

For 1b)
The question tells α³+β³ = 10n/m+5n²/m²
and you need to find another expression of α³+β³
so that you can show that (m+n)(2m+n)(4m+n)=0

Finally, practice make perfect !!

2014-11-03 01:49:17 補充:
* makes

2014-11-10 01:23:34 補充:
我建議你每次做嘅時候都諗番哥1課嘅concept

咁可能會令你諗到1D方法去做
2014-11-06 5:20 am
thank you Miss ! however, i found my enthusiasm towards math deteriorates due to increasing workload and the bad results every time i got
2014-11-03 6:13 pm
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