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A) dividing by 3 on either side gives the same equation as given in question stem ==> 3* 10y^2=3(x^2-4) ==> 3* 10^y = 3(x + 2)(x - 2) ==> Q B) diving by 2 on both side ==> 2* 10y^2=2 * (x-2)(x+2) ==> Q C) taking 4 to right hand side and solving ==> 10y^2=x^2 - 4 ==> 10y^2 = (x+2)(x-2) ==> Q D) multiplying both side by 2 ==> 10y^2=2x^2-4 ==> left hand side can't be factored to (x-2)(x+2). Hence, this is NOT equivalent to equation given in Q stem. We can stop here and mark option D. E) multiply both sides by 10 ==> 10 y^2=10 *(x^2-4)/10 ==> 10 y^2=(x^2-4) ==> 10 y^2=(x+2)(x-2)
** basic formula which should be known prior to solving this question =====> (A^2 - B^2) = (A+B)(A-B)
Other method to solve this Q is by substituting the values. The best value to take for "x" is 2 as it will make right hand side of the equation ZERO.
Re: Which of the following equations is NOT equivalent to 10y^2= [#permalink]
12 Sep 2012, 11:49
This post received KUDOS
Which of the following equations is NOT equivalent to 10y^2=(x+2)(x-2) ? (A) 30y^2=3x^2-12 (B) 20y^2=(2x-4)(x+2) (C) 10y^2+4=x^2 (D) 5y^2=x^2-2 (E) y^2=(x^2-4)/10
The original equation reduces to 10y^2 = x^2 -4 Option 1 - 3 times of equation Option 2 - 2 times of equation Option 3 - Same as original of equation Option 4 - Answer (Skip this option & jump to option 5, which in turn is right. Thus using POE this will be the answer. To cross check one can solve it) Option 5 - 1/10 times of equation Answer D
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