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e-GMAT Representative V
Joined: 04 Jan 2015
Posts: 3256
If 2 + √3 is one root of the equation, [m]x^2 - ax + b = 0[/m], ......  [#permalink]

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Difficulty:   45% (medium)

Question Stats: 59% (01:49) correct 41% (02:10) wrong based on 70 sessions

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If 2 + √3 is one root of the equation, $$x^2 - ax + b = 0$$, where a, b are positive numbers, then what is the value of a + b?

(A) 0
(B) 1
(C) 2√3
(D) 4
(E) 5

_________________

Originally posted by EgmatQuantExpert on 19 Jun 2019, 05:44.
Last edited by EgmatQuantExpert on 26 Jun 2019, 02:42, edited 1 time in total.
Intern  B
Joined: 27 Jun 2018
Posts: 14
Re: If 2 + √3 is one root of the equation, [m]x^2 - ax + b = 0[/m], ......  [#permalink]

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3
1
If one root of the quadratic equation is $$2+\sqrt{3},$$the other root is $$2-\sqrt{3}.$$Now, sum of roots = a = $$2+\sqrt{3}+2-\sqrt{3}$$ = 4
product of roots = b = $$(2+\sqrt{3})(2-\sqrt{3})$$= $$2^2 -{\sqrt{3}}^2$$ = 4-3 = 1
Hence, a + b = 4 + 1 = 5 (Option E)
GMAT Club Legend  V
Joined: 18 Aug 2017
Posts: 5918
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
Re: If 2 + √3 is one root of the equation, [m]x^2 - ax + b = 0[/m], ......  [#permalink]

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giving a try
$$x^2 - ax + b = 0$$,
so
we have ; (2+√3)^2- (2+√3)a+b=0
now value of a,b has to be such that eqn is 0
so let a= 4 and b=1
we get
7+4√3-8-4√3+1=0
sufficient
a+b = 4+1 ; 5
IMO E

EgmatQuantExpert wrote:
If 2 + √3 is one root of the equation, $$x^2 - ax + b = 0$$, where a, b are positive numbers, then what is the value of a + b?

(A) 0
(B) 1
(C) 2√3
(D) 4
(E) 5

e-GMAT Representative V
Joined: 04 Jan 2015
Posts: 3256
Re: If 2 + √3 is one root of the equation, [m]x^2 - ax + b = 0[/m], ......  [#permalink]

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Solution

Given:
• 2 + √3 is one root of the quadratic equation, $$x^2 - ax + b = 0$$
• a, b are positive numbers

To find:
• The value of a + b

Approach and Working Out:
• We are given that 2 + √3 is one root of the quadratic equation, $$x^2 - ax + b = 0$$
• And, we know that, if a +√ b is one root of a quadratic equation, then the other root will be a - √b.
o Thus, 2 + √3, and 2 - √3 are the two roots

• Now, from the given quadratic equation, $$x^2 - ax + b = 0$$
o Sum of the roots = -(-a) = a = (2 + √3) + (2 - √3) = 4
o Product of the roots = b = (2 + √3) * (2 - √3) = 4 – 3 = 1

• Therefore, a + b = 4 + 1 = 5

Hence, the correct answer is Option E.

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Posts: 1332
Location: India
Concentration: Entrepreneurship, Marketing
WE: Education (Education)
Re: If 2 + √3 is one root of the equation, [m]x^2 - ax + b = 0[/m], ......  [#permalink]

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EgmatQuantExpert wrote:
If 2 + √3 is one root of the equation, $$x^2 - ax + b = 0$$, where a, b are positive numbers, then what is the value of a + b?

(A) 0
(B) 1
(C) 2√3
(D) 4
(E) 5

If 1 root is x + sqrt(y)
The other root will be x - sqrt(y)

So other root is 2 - 3^1/2

a = sum of roots = 4
b = product of roots = 4 - 3 = 1

a + b = 5

Option E

Posted from my mobile device Re: If 2 + √3 is one root of the equation, [m]x^2 - ax + b = 0[/m], ......   [#permalink] 26 Jun 2019, 03:53
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# If 2 + √3 is one root of the equation, [m]x^2 - ax + b = 0[/m], ......  