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(2x+7)(4x-7)=21
We move all terms to the left:
(2x+7)(4x-7)-(21)=0
We multiply parentheses ..
(+8x^2-14x+28x-49)-21=0
We get rid of parentheses
8x^2-14x+28x-49-21=0
We add all the numbers together, and all the variables
8x^2+14x-70=0
a = 8; b = 14; c = -70;
Δ = b2-4ac
Δ = 142-4·8·(-70)
Δ = 2436
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}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$
The end solution:
$\sqrt{\Delta}=\sqrt{2436}=\sqrt{4*609}=\sqrt{4}*\sqrt{609}=2\sqrt{609}$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(14)-2\sqrt{609}}{2*8}=\frac{-14-2\sqrt{609}}{16} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(14)+2\sqrt{609}}{2*8}=\frac{-14+2\sqrt{609}}{16} $
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