OG详解-OG4 数学1 Q3

Choice B is correct. Multiplying the left- and right-hand sides of the given equation by 25 yields x² = 900. Taking the square root of the left- and right-hand sides of this equation yields x = 30  or x = -30. Of these two solutions, only 30 is given as a choice.
Choice A is incorrect. This is a solution to the equation  x² = 36. Choice C is incorrect and may result from conceptual or calculation errors. Choice D is incorrect and may result from conceptual or calculation errors.