函数f(x)=3x方 2(k-1)x k 5在区间(0,2)n内有l零点求k的取值范围是3x方+2(k-1)
问题描述:
函数f(x)=3x方 2(k-1)x k 5在区间(0,2)n内有l零点求k的取值范围
是3x方+2(k-1)
答
f(x)=3x²+2(k-1)x+k+5在区间(0,2)内有1零点,则:
(1) △=4(k-1)²-4*3(k+5)≥0时,得:k≥7或k≤-2
(2)f(0)*f(2)综上得:-5
f(x)=3x²+2(k-1)x+k+5在区间(0,2)内有2零点,则:
(1) △=4(k-1)²-4*3(k+5)>0时,得:k>7或k<-2
(2)x=0时,3x²+2(k-1)x+k+5>0,k>-5;
(3)x=2时,3x²+2(k-1)x+k+5>0,k>-13/5;
综上得:k>7或-13/5
答
f(x)=3x^2+2(k-1)x+k+5在区间(0,2)内有零点,则:
f(0)f(2)即(k+5)(12+4(k-1)+k+5)(k+5)(5k+13)所以-5
答
f(x)=3x²+2(k-1)x+k+5在区间(0,2)内有零点,则:
(1)判别式=4(k-1)²-12(k+5)=0时,得:k=7或者k=-2,此时方程的根分别是:
k=7时,根是:x1=x2=-2
k=-2时,根是:x1=x2=1
(2)若判别式大于0,则:k>7或k0、f(2)>0,得:此时无解;
②若在(0,2)内存在一个根,则:f(0)×f(2)