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3y² + 2y - 1

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3y² + 2y - 1

by harsh.champ » Fri Feb 19, 2010 10:20 am
What is the value of 3y² + 2y - 1 ?

1. y² + 2y = 0
2. y = -2
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by thephoenix » Fri Feb 19, 2010 10:26 am
harsh.champ wrote:What is the value of 3y² + 2y - 1 ?

1. y² + 2y = 0
2. y = -2
IMO B

1) inserting in q we r left with 2y^2-1 which can have infinite value
insuff

2) suff

exp=7

hence B
Last edited by thephoenix on Fri Mar 05, 2010 8:23 pm, edited 1 time in total.
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by shashank.ism » Sun Feb 21, 2010 6:57 am
harsh.champ wrote:What is the value of 3y² + 2y - 1 ?

1. y² + 2y = 0
2. y = -2
St.1) y² + 2y = 0
--> 3y² + 2y - 1 = 2y²+ (y² + 2y) - 1 =0 = 2y² -1
y² + 2y = 0 --> y=0,-2 so two values not suff...

St.2) y = -2 --> 3y² + 2y - 1 = 3x4 +2x-2 -1 = 7 .....suff..

Ans B
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by dbaner1 » Fri Mar 05, 2010 3:34 pm
St1: Translate into factors of Y
3y^2+3y-y-1
3y(y+1) -1(y+1)
(3Y-1)(Y+1)
y = 1/3 or -1...Two solutions...Hence, not suff

St2: Just Plug Value of Y into original Equation

Ans: B
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by GMATSUCKER » Sat Mar 06, 2010 1:03 pm
Shashank.ism has given a good explanation. But I was curious, can't we take statement 1 as: Y^2 + 2Y = 0 as Y^2=-2Y
or Y = -2. Or is it necessary to solve the 1st statement as a quadratic equation.
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