OG详解-OG3 数学2 Q12

Choice C is correct. It’s given that f (x )= 8√x​ . Substituting 48 for f (x) in this equation yields 48 =  8√x . Dividing both sides of this equation by 8 yields 6 = √x​ . This can be rewritten as  √x​ = 6. Squaring both sides of this equation yields x = 36. Therefore, the value of x for which f ( )= 48 is 36.
Choice A is incorrect. If x = 6, f (x )= 8 √6​ , not 48. Choice B is incorrect. If x = 8, f (x)= 8√8​ , not 48. Choice D is incorrect. If x = 64, f (x )= 8 √64​, which is equivalent to 64, not 48.