A positive number, when decreased by 4, is equal to 21 times the reciprocal of the number. The number is:
Solution
Correct Answer: Option C
মনেকরি,
সংখ্যাটি = x
প্রশ্নমতে,
x - 4 = 21/x
বা, x(x - 4) = 21
বা, x2 - 4x - 21 = 0
বা, x2 - 7x + 3x - 21 = 0
বা, x(x - 7) + 3(x - 7) = 0
∴ (x - 7)(x + 3) = 0
হয়
x - 7 = 0
বা, x = 7
অথবা
x + 3 = 0
বা, x = - 3
∴ সংখ্যাটি = 7
সংখ্যাটি = x
প্রশ্নমতে,
x - 4 = 21/x
বা, x(x - 4) = 21
বা, x2 - 4x - 21 = 0
বা, x2 - 7x + 3x - 21 = 0
বা, x(x - 7) + 3(x - 7) = 0
∴ (x - 7)(x + 3) = 0
হয়
x - 7 = 0
বা, x = 7
অথবা
x + 3 = 0
বা, x = - 3
∴ সংখ্যাটি = 7
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