OG详解-OG8 数学1 Q8

Choice A is correct. For the linear function f, it’s given that f(7)= 28. Substituting 7 for x and 28 for f(x) in the given function yields 28 = 4(7) +b, or 28 = 28+b. Subtracting 28 from each side of this equation yields 0 = b. Therefore, the value of b is 0.
Choice B is incorrect. Substituting 1 for b in the given function yields f(x)= 4x+1.   For this function, when the value of x is 7, the value of f(x) is 29, not 28. Choice C is incorrect. Substituting 4 for b in the given function yields f(x)= 4x+4. For this function, when the value of x is 7, the value of f(x) is 32, not 28. Choice D is incorrect. Substituting 7 for b in the given function yields f(x)= 4x+7. For this function, when the value of x is 7, the value of f(x) is 35, not 28.