I stopped when I had two equation involving A&B thinking A and B will have multiple answer and close E.
For DS do we always need to find complete solution bec looking at the equation one might interpret that this equation would have multiple ans hence information is not sufficient.
udaymathapati wrote:
At what two points does the graph of y = (x+a)(x+b) intersect the x axis?
You don't need to worry what the equation represents. Just think, what does 'intersection with x axis' imply? It means the y co-ordinate is 0.
0 = (x+a)(x+b)
or x = -a or -b
Hence the graph must intersect the x axis at points (-a, 0) and (-b, 0). We need the values of a and b now.
Statement 1: a + b = -1
Two variables, only one equation. Not sufficient.
Statement 2: Graph intersects the y axis at (0, -6).
At y axis, x = 0. This means when x = 0, y co-ordinate is -6.
Put these values in y = (x+a)(x+b) to get -6 = ab.
Again, two variables, one equation. Not sufficient alone.
Using both statements, we have two variables and two different equations so we will be able to find the values of a and b. It doesn't matter which is 'a' and which is 'b'. We find that the two of them are -3 and 2. Since we need the points (-a, 0) and (-b, 0), the required points are (3, 0) and (-2, 0). Sufficient.
Answer (C).