OG详解-OG3 数学2 Q18

Choice A is correct. The given system of linear equations can be solved by the elimination method. Multiplying each side of the second equation in the given system by 3 yields (2x+2y)(3)=(10)(3), or 6x+6y = 30. Subtracting this equation from the first equation in the given system yields (6x+7y)-(6+6y)=(28)-(30), which is equivalent to (6x-6x)+(7y-6y)= 28-30, or y=-2.
Choice B is incorrect. This is the value of x , not the value of y. Choice C is incorrect and may result from conceptual or calculation errors. Choice D is incorrect and may result from conceptual or calculation errors.