A NATURAL NUMBER WHEN INCREASED BY 84 EQUALS 160 TIMES ITS RECIPROCAL.FIND THE NUMBER

42.   A natural number when increased by 84 equals 160 times its reciprocal. Find the number.           
                                                                                                                         [ NCERT EXEMPLAR]

Hello !
Let the natural positive number be x 
ATQ 
x + 84    = 160 ( 1/x) 
x² + 84x = 160 
x² + 84x - 160 = 0 

Here a quadratic equation formed :
Where 
a (coefficient of x²) = 1 
b (coefficient of x ) = 84
c (constant           ) = -160
D (Discriminant    ) = b² - 4ac
                               = 84² - 4 x 1 x 160 
                               = 7056 + 640 
                               = 7696

we are finding roots (zeros) of the quadratic by this quadratic formula
-b+-√D/2a 
Two zeros are 

160 - √7696 / 2  and 160 + √7696 / 2

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