GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

 It is currently 05 Apr 2020, 15:14

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# (n+k)^2 - 2nk =

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:

### Hide Tags

Senior PS Moderator
Joined: 26 Feb 2016
Posts: 3258
Location: India
GPA: 3.12
(n+k)^2 - 2nk =  [#permalink]

### Show Tags

29 Oct 2018, 23:23
00:00

Difficulty:

5% (low)

Question Stats:

98% (00:30) correct 2% (00:11) wrong based on 46 sessions

### HideShow timer Statistics

$$(n+k)^2 - 2nk =$$

A. $$n^2 + k^2$$
B. $$n^2$$
C. $$0$$
D. $$n^2 - k^2$$
E. $$(n-k)^2$$

_________________
You've got what it takes, but it will take everything you've got
Senior Manager
Joined: 15 Feb 2018
Posts: 456
(n+k)^2 - 2nk =  [#permalink]

### Show Tags

29 Oct 2018, 23:43
$$(n+k)^2$$
This is a 'square of a sum' quadratic. It follows this formula
$$(n+k)^2$$=$$n^2+2nk+k^2$$

Inserting that back into the equation
$$n^2+2nk+k^2$$-2nk

=$$n^2+2nk-2nk+k^2$$

=$$n^2+k^2$$

A
GMAT Club Legend
Joined: 11 Sep 2015
Posts: 4587
GMAT 1: 770 Q49 V46
Re: (n+k)^2 - 2nk =  [#permalink]

### Show Tags

21 Feb 2019, 12:44
Top Contributor
pushpitkc wrote:
$$(n+k)^2 - 2nk =$$

A. $$n^2 + k^2$$
B. $$n^2$$
C. $$0$$
D. $$n^2 - k^2$$
E. $$(n-k)^2$$

My approach would have been the same as that provided by philipssonicare

That said, we can also solve this problem by plugging in values and evaluating

Here's what I mean.

If n = 2 and k = 1, then:
(n + k)² - 2nk = (2 + 1)² - 2(2)(1)
= 3² - 4
= 9 - 4
= 5
So, when n = 2 and k = 1, (n + k)² - 2nk = 5

This means the answer choice that is EQUIVALENT to (n + k)² - 2nk must also equal 5 when n = 2 and k = 1

Let's check the answer choices...
A. n² + k² = 2² + 1² = 5 PERFECT - keep
B. n² = 2² = 4. No good. We need 5. ELIMINATE.
C. 0 No good. We need 5. ELIMINATE.
D. n² - k² = 2² - 1² = 3. No good. We need 5. ELIMINATE
E. (n - k)² = (2 - 1)² = 1. No good. We need 5. ELIMINATE

By the process of elimination, the correct answer is A

Cheers,
Brent
_________________
Test confidently with gmatprepnow.com
Re: (n+k)^2 - 2nk =   [#permalink] 21 Feb 2019, 12:44
Display posts from previous: Sort by

# (n+k)^2 - 2nk =

 new topic post reply Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne