GRE Prep 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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
GRE Prep Club Team Member
Joined: 20 Feb 2017
Posts: 2508
Given Kudos: 1053
GPA: 3.39
If (Z-3)^2 = 12,then 2z(z-6)=
[#permalink]
08 Feb 2020, 05:59
08 Feb 2020, 05:59
Expert Reply
00:00
Question Stats:
100% (01:58) correct
0% (00:00) wrong based on 5 sessions
Hide Show timer Statistics
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: If (Z-3)^2 = 12,then 2z(z-6)=
[#permalink]
08 Feb 2020, 06:39
08 Feb 2020, 06:39
1
GeminiHeat wrote:
If \((z-3)^2 = 12\),then \(2z(z-6)=\)
A. 6
B. 9
C. 10
D. 15
E. 27
A. 6
B. 9
C. 10
D. 15
E. 27
There are two possible approaches here:
1) Solve the original equation for z, and then plug that value into \(2z(z-6)\)
2) Take the original equation, \((z-3)^2 = 12\), and manipulate it so that it looks like \(2z(z-6)\)
Let's go with approach #2
Given: \((z-3)^2 = 12\)
Expand and simplify the left side: \(z^2-6z+9=12\)
Multiply both sides of the equation by 2 to get: \(2z^2-12z+18=24\)
Subtract 18 from both sides to get: \(2z^2-12z=6\)
Back to the left side: \(2z(z-6)=6\)
Answer: A
Cheers,
Brent
GRE Instructor
Joined: 19 Jan 2020
Status:Entrepreneur | GMAT, GRE, CAT, SAT, ACT coach & mentor | Founder @CUBIX | Edu-consulting | Content creator
Posts: 117
Given Kudos: 0
GPA: 3.72
Re: If (Z-3)^2 = 12,then 2z(z-6)=
[#permalink]
09 Feb 2020, 07:50
09 Feb 2020, 07:50
1
GeminiHeat wrote:
If \((z-3)^2 = 12\),then \(2z(z-6)=\)
A. 6
B. 9
C. 10
D. 15
E. 27
A. 6
B. 9
C. 10
D. 15
E. 27
Method 1
\((z-3)^2 = 12\)
\(=> z^2 - 6x + 9 = 12\)
\(=> z^2 - 6x = 3\)
\(=> z(z - 6) = 3\)
\(=> 2z(z - 6) = 2 * 3 = 6\)
Answer A
Method 2:
Let us approximate (or use a calculator!):
\((z-3)^2 = 12\)
\(=> z - 3 = \sqrt{12} = \sqrt{(3 * 4)} = 2 * \sqrt{3} = 2 * 1.7 = 3.4\)
\(=> z = 6.4\)
\(=> 2z(z - 6) = 2 * 6.4 * (6.4 - 6) = 12.8 * 0.4 =~ 13 * 0.4 = 5.2\)
=> Best Option is A (= 6)
