OG详解-OG9 数学2 Q10

Choice D is correct. The given function f is a linear function. Therefore, the graph of y=f(x) in the xy-plane has one x-intercept at the point (k,0), where k is a constant. Substituting 0 for f(x) and k for x in the given function yields  0=7k-84. Adding 84 to both sides of this equation yields 84=7k. Dividing both sides of this equation by 7 yields 12=k. Therefore, the x-intercept of the graph of y =f(x) in the xy-plane is (12,0).
Choice A is incorrect and may result from conceptual or calculation errors. Choice B is incorrect and may result from conceptual or calculation errors. Choice C is incorrect and may result from conceptual or calculation errors.