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The range of the function `f(x) = log_(3) (5+4x - x^(2))`, isA. `(0, 2 ]`B. `(-oo, 2]`C. `(0, 9]`D. none of these

Answer» Correct Answer - B
For f(x) to be real, we must have
`5 + 4x - x^(2) gt 0`
`rArr x^(2) - 4x - 5 lt 0 rArr - 1 lt x lt 5`
Now, let `y = f(x)`. Then ,
`y = log_(3) (5+4x -x^(2))`
`rArr 3^(y) = 5+ 4x -x^(2)`
`x^(2) -4x + 3^(y) - 5=0`
`rArr x= (4pmsqrt(16-4.3^(y) + 20))/(2) rArr = 2 pm sqrt(9-3y)`
For x to be real, we have must have
`9-3^(y) ge 0 rArr 3^(y) ge 9 rArr le rArr y le 2`
Also , `y to - oo` as `x to -1 or 5`
Hence, range of `(f) = (-oo,2]`


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