• Difficult Problems in mathematics From post utme (ABU 2008)

    Mathematics

    Chima Sunday (Tutor)
    17-05-2016 12:54:00 +0000

    Hey friends! Checkout this mathematics questions, about 70% of students that attempted it got it wrong. Try it and see if you can get it right

    1. X*Y = XY - Y2; Evaluate (2x + y)*(y + 2x)
    A. 4xy
    B. 4x2
    C. 0
    D. 1

    Updated Solution
    X*Y = XY - Y2
    here X = (2x + y), and Y = (y + 2x) = (2x + y)
    thus X*Y = (2x + y)(2x + y) - (2x + y)2
    = (2x + y)2 - (2x + y)2
    = 0, so answer is Option C

    2. Evaluate x2 + 1/x2 if x - 1/x = 5
    A. 24
    B. 25
    C. 26
    D. 27

    Updated Solution
    x2 + 1/x2 = ?
    but x - 1/x = 5
    now sqauring both side
    (x - 1/x)2 = 52
    (x - 1/x)(x - 1/x) = 25
    x2 + 1/x2 - 2 = 25
    x2 + 1/x2 = 25 + 2 = 27
    So answer is Option D

    3. If (2x - 1)(2x + 3) + (2x + 1) = ax2 + bx + c; Find a,b,c
    A. 0,6,6
    B. 8,0,0
    C. 8,0,6
    D. 4,6,-2

    Updated Solution
    (2x - 1)(2x + 3) + (2x + 1) = a2 + bx + c
    opening the bracket
    4x2 + 6x - 2 - 3 + 2x + 1 = ax2 + bx + c 4x2 + 6x - 2 = ax2 + bx + c
    so by comparison
    a = 4
    b = 6
    c = -2
    so answer is Option D



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