OG详解-OG7 数学1 Q30

Choice D is correct. It’s given that the function f is defined by f(x) = 1​2​ (x+6). Substituting 4 for x in the given function yields f(4) =1​2​ (4+6), or f(4) = 5. Therefore, the value of f(4) is 5. Choice A is incorrect. This is the value of 2(4+6), not 1​2​ (4+6). Choice B is incorrect. This is the value of 2+(4+6), not1​2​ (4+6). Choice C is incorrect. This is the value of 4+6, not 1​2​ (4+6).