(x+7)(x-3)=-7

Question

solve it by quadratic equation standard form

Answer 1

FOIL, combine terms, and then use quadratic equation to solve:

 

x² - 3x + 7x - 21 = -7

x² + 4x - 21 = -7

x² + 4x - 21 + 7 = 0

x² + 4x - 14 = 0

 

so a=1, b=4, and c=-14

 

x = (-b ± √(b² - 4ac)) / 2a = (-4 ± √(4² - 4*1*-14)) / 2*1 = (-4 ± √(16 + 56)) / 2 = (-4 ± √(72)) / 2

   = (-4 ± √(36*2)) / 2 = (-4 ± 6√2) / 2 = -2 ± 3√2

 

Answer 2

Hi Kamran,

 

Try multiplying (x+7) and (x-3).  Then group all the terms on the left side of the equation and combine like terms.  Then you will have the standard form a(x^2)+b(x) + c = 0.  Remember that a, b and c are constants.  The final solution can be found with the quadratic formula x = (-b ± √(b²- 4ac))/2a  [negative b plus or minus the square root of b squared minus 4ac, all over 2a]