New Enroll in RBI Grade B New Batch - Starts on May 21

    Question

    If x = (√13 + √12)/ (√13 - √12) and y = (√13 -

    √12)/(√13 + √12), then find the value of 4x2 – xy + 4y2.
    A 2361 Correct Answer Incorrect Answer
    B 2491 Correct Answer Incorrect Answer
    C 2721 Correct Answer Incorrect Answer
    D 2541 Correct Answer Incorrect Answer

    Solution

    4x2 – xy + 4y2 4(x2 + y2) – xy 4[(x + y)2 – 2xy] – xy 4(x + y)2 – 9xy ……..(1) x + y = [(√13 + √12)/(√13 - √12)] + [(√13 - √12)/(√13 + √12)] = [(√13 + √12)2 + (√13 - √12)2]/((√13)2 - (√12)2) = [13 + 12 + 2(√13)(√12) + 13 + 12 - 2(√13)(√12)]/2 = 25   xy= [(√13 + √12)/(√13 - √12)][(√13 - √12)/(√13 + √12)] = 1 From eq (1) => 4(25)2 - 9 = 2491  

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