Given equation can also be written as
y=x^2+x(a+b)+ab --eq1
1) a+b=-1
hence y=x^2-x+ab
when y=0
x^2 - x = -ab --eq2
we dont know ab or a or bhence INSUFF
2) substituting x=0 and y=-6 in eq1
-6 = 0+0+ab
Still INSUFF
combining we get
from eq1 and eq2
x^2 - x = 6
or x^2-x-6=0
we can solve for x hence SUFF
hence C
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Source: Beat The GMAT — Data Sufficiency |
Hey, can you please tell me , why did u try with putting Y=0 for statement 1 in line 3. I am not able to get the reason for this substitution.
tryin700 wrote:Given equation can also be written as
y=x^2+x(a+b)+ab --eq1
1) a+b=-1
hence y=x^2-x+ab
when y=0
x^2 - x = -ab --eq2
we dont know ab or a or bhence INSUFF
2) substituting x=0 and y=-6 in eq1
-6 = 0+0+ab
Still INSUFF
combining we get
from eq1 and eq2
x^2 - x = 6
or x^2-x-6=0
we can solve for x hence SUFF
hence C
When the graph of y = (x+a)(x+b) meets X-axis, y value will be equal to ZERO. Hence y was equated to ZERO.
PS: y value will always be ZERO on X-axis.
PS: y value will always be ZERO on X-axis.
