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(3x-7)(3x+9)=0
We multiply parentheses ..
(+9x^2+27x-21x-63)=0
We get rid of parentheses
9x^2+27x-21x-63=0
We add all the numbers together, and all the variables
9x^2+6x-63=0
a = 9; b = 6; c = -63;
Δ = b2-4ac
Δ = 62-4·9·(-63)
Δ = 2304
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$$\sqrt{\Delta}=\sqrt{2304}=48$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-48}{2*9}=\frac{-54}{18} =-3 $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+48}{2*9}=\frac{42}{18} =2+1/3 $
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