A) 3/4
B) 2/3
C) 4/3
D) 4/5
Correct Answer: C
Solution :
\[(3x-4)(5x+7)=15{{x}^{2}}-ax-28,\] \[a-b=\frac{1}{2-\sqrt{3}}-\frac{1}{2+\sqrt{3}}=\frac{2+\sqrt{3}-2+\sqrt{3}}{(2-\sqrt{3})(2+\sqrt{3})}=\frac{2\sqrt{3}}{4-3}=2\sqrt{3}\] Now, \[{{\left( \frac{a+b}{a-b} \right)}^{2}}={{\left( \frac{4}{2\sqrt{3}} \right)}^{2}}=\frac{16}{4\times 3}=\frac{4}{3}.\]
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