The difference between a number and its square is 72 .What is the number ?

A 19

B 18

C 30

D 9

Solution

Correct Answer: Option D

মনে করি ,সংখ্যাটি =x
প্রশ্নমতে,
   x²-x=72
বা,x²-x-72 =0
বা, x²-9x+8x-72 =0
বা,x(x-9)+8(x-9)=0
বা,(x-9)(x+8)=0
∴ x =9 [since x ≠ -8]

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