g(x)=-1+4x+kx^2 g(-2)=3 求k

-1 + 4(-2) + k(-2)^2 = 3
-1 - 8 + 4k = 3
4k = 12
k = 3

2006-10-25 21:30:30 補充：
Maybe the answer is wrong.Cause: Checkingif k = 3g(x) = -1 4x 3x^2g(-2) = -1 4(-2) 3(-2)^2= -1 - 8 12= 3if k = -3g(x) = -1 4x (-3)x^2g(-2) = -1 4(-2) (-3)(-2)^2= -1 - 8 - 12= -21

2006-10-25 21:33:13 補充：
I think the plus sign can't be listed out during this 補充, sorry

由於g(-2)=3
所以:g(-2)= -1+4(-2)+k(-2)^2 =3
-1-8+4k^2=3
-9+4k^2=3
4k^2=12
k=3

你冇計錯 ... 如果sub k=-3
g(-2)=-1+4(-2)-3(-2)^2=3
-9-12=3
-21係唔等於3 ...

所以answer 唔係-3 係 3 ...