唔該~我想知道呢條題目點計呀!列埋步驟丫唔該^^

1.20-4c+5c-c*c
2.20+c-c既2次方

(4+c)(5-c)
(4x5,之後4x(-c),之後c x5,之後c x c)so
=20-4c+5c-c^2
(約簡)
=20-9c-c^2
(變做descending order)
=-c^2-9c+20

(4+c)(5-c)=

4x5 + 4x(-c) + (cx5) + c(-c)=
20-4c+5c-c2=

20+c-c2




*c2 is c square

(4+c)(5-c)
=4*5-4c+5c-c*c
=20+9c-c*c

2007-10-31 17:38:34 補充：
=20+c-c*c

展開?
(4+c)(5-c)
=20-4c+5c-c^2
=20+c-c^2

(4+c)(5-c)
=(4x5+5xc)-(4xc+cxc)
=20+5c-4c-cxc
=20+c-c^2