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by AJWILL » Sun Jul 15, 2012 1:07 pm
for the function y= ax^2 + bx +c. is b=0?
1)f(1)=f(-1)=0
2)f(1)=f(0)=0

thanks
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Source: — Data Sufficiency |
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by eagleeye » Sun Jul 15, 2012 3:37 pm
AJWILL wrote:for the function y= ax^2 + bx +c. is b=0?
1)f(1)=f(-1)=0
2)f(1)=f(0)=0

thanks
We have y= f(x) = ax^2+bx+c , we need to find whether b=0, let's look at the statements.
1.
f(1) = a+b+c = 0 (substitute x by 1 in f(x) = ax^2+bx+c )
f(-1)= a-b+c = 0
Subtracting the 2 equations above we get, 2b = 0. Hence b=0. Sufficient

2.
f(1) = a+b+c = 0
f(0) = c =0
Subtracting the two equations, we get:
a+b = 0 => b=-a. So b depends on a. Hence insufficient.

A is correct.

Let me know if this helps :)
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