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245=28x-0.4x^2
We move all terms to the left:
245-(28x-0.4x^2)=0
We get rid of parentheses
0.4x^2-28x+245=0
a = 0.4; b = -28; c = +245;
Δ = b2-4ac
Δ = -282-4·0.4·245
Δ = 392
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}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$
The end solution:
$\sqrt{\Delta}=\sqrt{392}=\sqrt{196*2}=\sqrt{196}*\sqrt{2}=14\sqrt{2}$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-28)-14\sqrt{2}}{2*0.4}=\frac{28-14\sqrt{2}}{0.8} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-28)+14\sqrt{2}}{2*0.4}=\frac{28+14\sqrt{2}}{0.8} $
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