[6]:下列敘述哪些是正確的?
Hatua BP Bapor
X (1)若二次函數f(x)滿足 (4+t) = f(-2-1),則f(x)在x=1時有最小值
X(2)已知f(x +6)-f(x-6)為四次多項式,則f(x)為四次多項式
(3)對於所有aeR,f(x) = x(x-1)(x+a)- 3x+1=0必有3個實根
(4)若函數f(x)滿足了(7) = f(17) = f(27) = 5,则f(37) =5 ax+bx+c 3
O
(5)已知a,b,cER,若 ax + (b-3)x+(c-2)>0恆成立,則
y = f(x) = ax? +bx+c 1874 y = 3x +2 E5 axbX-3X+C-2>0
Sol: (1)錯→因子(4+t) = f(-2-t),對稱軸為x=
(4+t) + (-2-t)
=1,但無法
2
判斷開口向上或向下,故f(x)在x=1時,未必有最小值
(2)錯→ f(x +6)-f(x-6) 為次多項式,則(x) 為五次多項式
(3)對f(x) = _x(x-1)(x + a) - 3x+1=x+(a-1)x-(a+3)x+1=0
因deg f(x)=3,f(o)>0,f(1) = -2 <0,f(0) =1>0,由
勘根定理知,f(x) =0必有3個實根
(4)錯令f(x) = (x-7)(x-17)(x-27) ·p+5 (p=0),故f(37) +5
(5)對→ ax* + (b-3)x + (C-2)>0ax' + bx +C> 3x +2,即
y = f(x) = ax + bx+c恆在y= 3x+2上方