In the xy plane, at what two points does the graph of y=(x+a)(x+b) intersect the x-axis?
1 - a + b = -1
2 - The graph intersects the y-axis at (0,-6)
this is a GMATPrep question
Got C too.
From the question, we know that the two values that we need to find are a and b.
(1) -a+b = 1, doesn't tell much. INSUFFICIENT.
(2) plug in x=0, you have -6 = a*b
Together, two equations, two unknowns. SUFFICIENT.