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Algebra
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If $$a = \frac{{\sqrt 5 + 1}}{{\sqrt 5 - 1}}$$   & $$b = \frac{{\sqrt 5 - 1}}{{\sqrt 5 + 1}}{\text{,}}$$    then the value of $$\frac{{{a^2} + ab + {b^2}}}{{{a^2} - ab + {b^2}}}{\text{ is?}}$$

Answer & Solution
Correct Answer: Option B
$$\eqalign{ & a = \frac{{\sqrt 5 + 1}}{{\sqrt 5 - 1}} \cr & b = \frac{{\sqrt 5 - 1}}{{\sqrt 5 + 1}}{\text{ }} \cr & \therefore a = \frac{1}{b} \cr & a + b = a + \frac{1}{a} \cr & \Rightarrow \frac{{\sqrt 5 + 1}}{{\sqrt 5 - 1}}{\text{ + }}\frac{{\sqrt 5 - 1}}{{\sqrt 5 + 1}} \cr & \Rightarrow \frac{{5 + 1 + 2\sqrt 5 + 5 + 1 - 2\sqrt 5 }}{{{{\left( {\sqrt 5 } \right)}^2} - {{\left( 1 \right)}^2}}} \cr & \Rightarrow \frac{{6 + 2\sqrt 5 + 6 - 2\sqrt 5 }}{{5 - 1}} \cr & \Rightarrow \frac{{12}}{4} \cr & \Rightarrow 3 \cr & \therefore \frac{{{a^2} + ab + {b^2}}}{{{a^2} - ab + {b^2}}} \cr & \Rightarrow \frac{{{a^2} + \frac{1}{{{a^2}}} + ab}}{{{a^2} + \frac{1}{{{a^2}}} - ab}} \cr & \Rightarrow a + \frac{1}{a} = 3 \cr & \Rightarrow {a^2} + \frac{1}{{{a^2}}} \cr & \Rightarrow 9 - 2 \cr & \Rightarrow 7\left( {ab = 1} \right) \cr & \therefore \frac{{{a^2} + \frac{1}{{{a^2}}} + ab}}{{{a^2} + \frac{1}{{{a^2}}} - ab}} \cr & = \frac{{7 + 1}}{{7 - 1}} \cr & = \frac{8}{6} \cr & = \frac{4}{3} \cr} $$
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2 Comments
Salim Hossain
Salim Hossain 2 years ago
Here ab=1
& (a+b)=√5+1√5−1+√5−1√5+1
⇒(a+b)=(√5+1)2+(√5−1)24
=5+1+2√5+5+1−254
⇒(a+b)=3
(a2+b2)=(a+b)2−2ab
=9−2=7
∴a2+b2+aba2+b2−ab=7+17−1=43
Rafi Dark
Rafi Dark 4 years ago
Correct option is A)
Here ab=1
& (a+b)= 3
a^2+b^2 = (a+b)^2-2ab =9-2=7
(a^2+b^2+ab)/(a^2+b^2-ab)=(7+1)/(7-1)=8/6=4/3
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