hamburger menu
All Coursesall course arrow
adda247
reward-icon
adda247
    arrow
    arrow
    arrow
    If 7+2511+35\frac{7 + 2\sqrt{5}}{11 + 3\sqrt{5}}11+35​7+25​​  = a + b5\sqrt{5}5​, then:​
    Question

    If 7+2511+35\frac{7 + 2\sqrt{5}}{11 + 3\sqrt{5}}  = a + b5\sqrt{5}, then:​

    A.

    a = 1 ; b = 5\sqrt{5}​​

    B.

    a = 5;b=1\sqrt{5} ; b = 1​​

    C.

    a=116;b=4776a = \frac{1}{16} ; b = \frac{47}{76}​​

    D.

    a=4776;b=176a = \frac{47}{76} ; b = \frac{1}{76}​​

    Correct option is D

    Given:

    7+2511+35\frac{7 + 2\sqrt{5}}{11 + 3\sqrt{5}} = a + b5\sqrt{5}

    Solution:

    To rationalize the denominator, we multiply by the conjugate of the denominator.

    (7+25)(1135)(11+35)(1135)=>7×11+7×(35)+25×11+25×(35)112(35)2=>77215+2253012145=>47+576=>4776+1765\begin{aligned}& \frac{(7+2 \sqrt{5})(11-3 \sqrt{5})}{(11+3 \sqrt{5})(11-3 \sqrt{5})} \\& \Rightarrow \frac{7 \times 11+7 \times(-3 \sqrt{5})+2 \sqrt{5} \times 11+2 \sqrt{5} \times(-3 \sqrt{5})}{11^2-(3 \sqrt{5})^2} \\& \Rightarrow \frac{77-21 \sqrt{5}+22 \sqrt{5}-30}{121-45} \\& \Rightarrow \frac{47+\sqrt{5}}{76} \\& \Rightarrow \frac{47}{76}+\frac{1}{76} \sqrt{5}\end{aligned}    

    Comparing with a + b5\sqrt{5} 

    a = 4776\frac{47}{76} , b =176\frac{1}{76}​​

    Thus, the correct answer is (D)

    Free Tests

    Free
    Must Attempt

    CBT-1 Full Mock Test 1

    languageIcon English
    • pdpQsnIcon100 Questions
    • pdpsheetsIcon100 Marks
    • timerIcon90 Mins
    languageIcon English
    Free
    Must Attempt

    RRB NTPC Graduate Level PYP (Held on 5 Jun 2025 S1)

    languageIcon English
    • pdpQsnIcon100 Questions
    • pdpsheetsIcon100 Marks
    • timerIcon90 Mins
    languageIcon English
    Free
    Must Attempt

    CBT-1 General Awareness Section Test 1

    languageIcon English
    • pdpQsnIcon40 Questions
    • pdpsheetsIcon30 Marks
    • timerIcon25 Mins
    languageIcon English

    Similar Questions

    test-prime-package

    Access ‘RRB NTPC’ Mock Tests with

    • 60000+ Mocks and Previous Year Papers
    • Unlimited Re-Attempts
    • Personalised Report Card
    • 500% Refund on Final Selection
    • Largest Community
    students-icon
    353k+ students have already unlocked exclusive benefits with Test Prime!
    Our Plans
    Monthsup-arrow