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x(4x+7)=400
We move all terms to the left:
x(4x+7)-(400)=0
We multiply parentheses
4x^2+7x-400=0
a = 4; b = 7; c = -400;
Δ = b2-4ac
Δ = 72-4·4·(-400)
Δ = 6449
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}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(7)-\sqrt{6449}}{2*4}=\frac{-7-\sqrt{6449}}{8} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(7)+\sqrt{6449}}{2*4}=\frac{-7+\sqrt{6449}}{8} $
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