OG详解-OG10 数学2 Q10

Choice B is correct. Since the point (x, y) is an intersection point of the graphs of the given equations in the xy-plane, the pair (x, y) should satisfy both equations,   and thus is a solution of the given system. According to the first equation, y = 76.  Substituting 76 in place of y in the second equation yields x² -5 = 76. Adding 5  to both sides of this equation yields x² = 81. Taking the square root of both sides of this equation yields two solutions: x = 9 and x = -9. Of these two solutions, only -9 is given as a choice.
Choice A is incorrect and may result from conceptual or calculation errors. Choice C is incorrect and may result from conceptual or calculation errors.  Choice D is incorrect. This is the value of coordinate y, rather than x, of the intersection point (x, y).