Question

the sum of the roots of x2 - 8x - 9 = 0 is ______​

Answer 1

Step-by-step explanation:

Method:

sum of the roots =−

a

b

=−

1

7

=−7

product of the roots =

a

c

=

1

9

=9

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Answer 2

$sum \: of \: roots \: = \frac{ - b}{a} \\ {x}^{2} - 8x - 9 = 0 \\ sum \: of \: roots = \frac{ - ( - 8)}{1} \\ sum \: of \: roots \: = 8$

HOW TO PROVE???

${x}^{2} - 8x - 9 = 0 \\ {x}^{2} - 9x + x - 9 = 0 \\ x(x - 9) + (x - 9) = 0 \\ (x - 9)(x + 1) = 0 \\ roots \: are \: \\ x - 9 = 0 \\ x = 9 \\ x + 1 = 0 \\ x = - 1 \\ sum \: = 9 + ( - 1) \\ 9 - 1 = 8$

HENCE, PROVED

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