How to solve q42 because from the option only 4 can be the value of x that is perfect square
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The question seems to have a typo or something. If X itself were being asked, then the answer would be 9, not 3, 4, or 5.
Let X = a² and X + 2491 = b².
Then,
b² - a² = 2491
⇒ (b - a)(b + a) = 2491 = 47 × 53
Taking b - a = 47 and b + a = 53,
2b = 100 ⇒ b = 50
a = 3
Hence, X = a² = 9, and 9 + 2491 = 2500 = 50².