I think what we're trying to do here is put the equation in y=mx+b form.
So first thing I would do before moving to the statements is to expand the (x+a)(x+b)
= x^2+ax+bx+ab
= x^2+(a+b)x+ab
Now, let's move onto our statements with the goal of finding (a+b) AND ab.
St 1) a+b =-1
- Tempting, but this gives us only one of our unknowns, not both so INSUFF
St 2) (0,-6) is a point on the graph
- so let's plug this point into our expanded formula
y = x^2+(a+b)x+ab
(-6) = 0^2 + (a+b)*(0) +ab
(-6) = ab
- again, tempting, but we don't know a+b from this equation, so INSUFF
Bringing the two together gives us both unknowns a+b AND ab
So answer C.
GMAT Prep - coordinate plane
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Source: Beat The GMAT — Data Sufficiency |
