F.2數學題

daisychan

原帖由 swallowngxx 於 08-9-23 22:37 發表


x=y=z都是相同, 我仔仔剛上中二, 未學過這數式, 但他計到, 唔知算唔算深.

Dear swallowngxx,

I'm afraid your son is conceptually wrong.
He forgot the statement that " x, y, z are any integers"

8x + 4y - 5z  is divisible by 7
Therefore,
16x + 8y - 10z is divisible by 7
16x + 8y - 10z - 7(x+y+z) is divisible by 7
i.e. 9x + y - 17z is divisible by 7
i.e. 9x + y - 17z +21z is divisible by 7
i.e. 9x +y + 4z is divisible by 7

I consider this question is difficult for most of the Form 2 students. Only the top 5% in Maths can tackle it.

[ 本帖最後由 daisychan 於 08-9-23 22:59 編輯 ]