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Retired Moderator Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 171

Kudos [?]: 2917 , given: 394

If (x – y) = and (x + y) = , what is the value of x2 – y2 [#permalink]
Expert's post 00:00

Question Stats: 81% (00:21) correct 18% (01:28) wrong based on 37 sessions
If $$(x - y) =\sqrt{12}$$ and $$(x + y) = \sqrt{3}$$, what is the value of $$x^2 - y^2$$?

(A) 3
(B) 6
(C) 9
(D) 36
(E) It cannot be determined from the information given.
[Reveal] Spoiler: OA

_________________

Sandy
If you found this post useful, please let me know by pressing the Kudos Button

Try our free Online GRE Test Retired Moderator Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 171

Kudos [?]: 2917  , given: 394

Re: If (x – y) = and (x + y) = , what is the value of x2 – y2? ( [#permalink]
1
KUDOS
Expert's post
Explanation

The factored form of the Difference of Squares (one of the “special products” you need to memorize for the exam) is comprised of the terms given in this problem:
$$x^2 - y^2 = (x + y)(x - y)$$

Substitute the values $$\sqrt{12}$$ and $$\sqrt{3}$$ in place of (x – y) and (x + y), respectively:

x^2 - y^2 = $$\sqrt{12} \times \sqrt{3}$$

Combine 12 and 3 under the same root sign and solve:
$$x^2 - y^2 =\sqrt{12} \times \sqrt{3}$$
$$x^2 - y^2 =\sqrt{36}$$
$$x^2 - y^2 = 6$$
_________________

Sandy
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Try our free Online GRE Test Re: If (x – y) = and (x + y) = , what is the value of x2 – y2? (   [#permalink] 18 Jul 2018, 07:16
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