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2x*x+9x-81=0
We add all the numbers together, and all the variables
9x+2x*x-81=0
Wy multiply elements
2x^2+9x-81=0
a = 2; b = 9; c = -81;
Δ = b2-4ac
Δ = 92-4·2·(-81)
Δ = 729
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{729}=27$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-27}{2*2}=\frac{-36}{4} =-9 $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+27}{2*2}=\frac{18}{4} =4+1/2 $
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