The function is y=2x this means that the solutions will have the form (x, y)=(x,2x). For example: (0,0),(1,2),(2,4),(3,6) are solutions. The first answer choice satisfies the above conditions. The second answer choice contains (2,2), and (2,6), both of which do not satisfy the (x,2x) condition, so it's not correct. The third answer choice contains (4,2), which again does not satisfy (x,2x), so not the right answer.
1/9 Here's the proper explanation: Since the vertex is (2,-1), the original equation will look like this: y=a*(x-2)^2-1 When the substitution happens we get to this: 0=a*(5-2)^2-1 then 1=a*(5-2)^2 -> 1=a*9 So, a=1/9! Written in another form: 1/9x^2-4/9x+4/9-1
