OG详解-OG2 数学1 Q19

Choice A is correct. The x-intercept of a graph in the xy-plane is the point onthe graph where y = 0. It’s given that function h is defined by h(x)= 4x +28.Therefore, the equation representing the graph of y = h (x) is  y = 4x +28. Substituting 0 for y in the equation y = 4x +28 yields 0 = 4x +28. Subtracting  28 from both sides of this equation yields -28 = 4x. Dividing both sides of this    equation by 4 yields -7 = x. Therefore, the x-intercept of the graph of y = h (x)  in the xy-plane is (-7, 0). It’s given that the x-intercept of the graph of  y = h (x) is (a, 0). Therefore, a =-7. They-intercept of a graph in the xy-plane is the point on the graph where x = 0. Substituting 0 for x  in the equation y = 4x +28 yields y = 4 (0)+28, or y = 28. Therefore, they-intercept of the graph of y = h (x) in the xy-plane is  (0, 28). It’s given that they-intercept of the graph of  y = h (x) is  (0, b). Therefore, b = 28. If a =-7 and b = 28, then the value of a + b  is -7 +28, or 21.

Choice B is incorrect. This is the value of b, not  a + b. Choice C is incorrect and may result from conceptual or calculation errors. Choice D is incorrect. This is the value of -a + b , not a + b.