Question 366606
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Hi, 
x(2x+5)=168 
2x^2 + 5x - 168 = 0
Yes, factoring works: 
Coming up with the product of -8*21 = 168 and using that
(2x +21)(x -8) = 0  
(2x + 21)=0
x = -(21/10) = -10.5
(x -8) = 0 
x = 8 
The quadratic equations "always" works as well:
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
{{{x = (-5 +- sqrt( 1369 ))/(4) }}}
{{{x = (-5 +- 37)/(4) }}}
x = (-5 + 37)/4 = 8
x = (-5 -37)/4 = -42/4 = -21/2 = -10.5