Q.

Find a natural number whose square diminished by 84 is equal to thrice of 8 more than the number.


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a

12

b

9

c

-9

d

-12 

answer is A.

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Detailed Solution

It is given, a natural number whose square diminished by 84 is equal to thrice of 8 more than the number.
Let the natural number be x.
x 2 84=3(x+8)  
x 2 84=3x+24  
x 2 3x8424=0  
x 2 3x108=0   x 2 12x+9x108=0  
x(x12)+9(x12)=0  
(x12)(x+9)=0  
Therefore, two values of x are
x=12 or x=−9
x=−9 is not a natural number so it can be ignored.
Therefore, the correct option is 1.
 
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