AAPL wrote:GMAT Prep
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 \((0, -6)\).
y = (x+a)(x+b)
y = x² + ax + bx + ab
y = x² + x(a+b) + ab
The calculate the x-intercepts, we need to know both a+b and ab.
Statement 1:
No information about ab.
INSUFFICIENT.
Statement 2:
Plugging x=0 and y=-6 into y = (x+a)(x+b), we get:
-6 = (0+a)(0+b)
-6 = ab
No information about a+b.
INSUFFICIENT.
Statements combined:
Since we know both a+b and ab, SUFFICIENT.
The correct answer is
C.
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