y(y+1)=6-(y-5)(-3)
y^2 +y = 15y-9
y^2 -14y +9 = 0
_______
-b ±√b^2 - 4ac
y = ------------------------
2a
______________
-(-14) ±√ (-14)^2 - 4(1)(9)
y = ------------------------------------
2(1)
________
14 ±√ 196 - 36
y = ------------------------------
2
___
17 ±√ 160
y = ------------------
2
17 +√ 160 17 -√ 160
y = ------------------ 或 ------------------
2 2
2.(k-3)(k+1/5)-1=2(k-1)
(5)((k-3)(k+1/5)-1)=2(5)(k-1)
(k-3)(5k+1)-5=10(k-1)
5k^2 +k -15k -3 -5 = 10k -10
5k^2 -14k -8 = 10k -10
5k^2 -24k +2 = 0
________
-b ± √ b^2 - 4ac
k = ---------------------------
2a
_____________
-(-24) ±√ (-24)^2 - 4(5)(2)
k = ---------------------------------------
2(5)
_______
24 ±√ 576 - 40
k = ----------------------------
10
____
24 ±√ 536
k = ------------------------
10
24 +√536 24 - √536
k = ----------------------- 或 --------------------------
10 10
數學神手做的數...沒錯吧?
[ 本帖最後由 tony987852 於 2010-9-25 08:27 編輯 ]