square roots doubt

This topic has expert replies
Junior | Next Rank: 30 Posts
Posts: 13
Joined: Sat Oct 03, 2015 1:46 pm

square roots doubt

by ahahkhyati.j » Mon Nov 23, 2015 4:41 pm
Hi,
Can someone please help me understand the following questions and how are they different?

1. If g(x) = 3x + x^1/2, what is the value of g(d2 + 6d + 9)?

In the above question they have taken both (d+3) and -(d+3) for x^1/2 to solve the equation

2. if x is negative and y is positive, what is (4x^2−4xy+y^2)^1/2
In this question it is mentioned that the number under root will only take positive value.


Can someone explain me what is the difference. From the rule i know if you have (x^2)^1/2 you can take both negative and positive values for x then shouldn't both these questions have both negative and positive value? Can someone please explain
thank you.

User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

by sanju09 » Wed Nov 25, 2015 2:57 am
ahahkhyati.j wrote:Hi,
Can someone please help me understand the following questions and how are they different?

1. If g(x) = 3x + x^1/2, what is the value of g(d2 + 6d + 9)?

In the above question they have taken both (d+3) and -(d+3) for x^1/2 to solve the equation

2. if x is negative and y is positive, what is (4x^2−4xy+y^2)^1/2
In this question it is mentioned that the number under root will only take positive value.


Can someone explain me what is the difference. From the rule i know if you have (x^2)^1/2 you can take both negative and positive values for x then shouldn't both these questions have both negative and positive value? Can someone please explain
thank you.
Power HALF refers to √, which means positive (by and large non-negative) root only; so NO - (d + 3) be considered. The basic function concepts are occasionally tested on GMAT. Remember, whatever is d + 3 or 2x - y in sign, positive or negative; their whole squares are non-negatives.
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

GMAT Instructor
Posts: 2630
Joined: Wed Sep 12, 2012 3:32 pm
Location: East Bay all the way
Thanked: 625 times
Followed by:119 members
GMAT Score:780

by Matt@VeritasPrep » Fri Nov 27, 2015 12:44 am
The first question seems flawed - do you have the complete text, with solutions? It'd be helpful to see.