已知函数f(x)=log3mx2+8x+nx2+1的定义域为R,值域为[0,2],求m.n的值.
已知函数f(x)=log3
的定义域为R,值域为[0,2],求m.n的值.
mx2+8x+n |
x2+1 |
数学人气:306 ℃时间:2019-08-19 18:34:17
优质解答
由于f(x)=log3mx2+8x+nx2+1的定义域为R,∵x2+1>0,故mx2+8x+n>0恒成立.令y=mx2+8x+nx2+1,由于函数f(x)的值域为[0,2],则 1≤y≤9,且(y-m)•x2-8x+y-n=0 成立.由于x∈R,①若y-m≠0,∴方程的判别式△=...
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