Решите систему уравнений! 21x^2 + 39x

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21x² + 39x - 6 = 0
D=39²-4*21*(-6)=1521+504=2025=45²
x₁=(-39+45)/2*21=1/7
x₂=(-39-45)/2*21=-2
x∈(-2;1/7)
$\left \{ {{21 x^{2} + 39x - 6 \ \textless \ 0} \atop {x\ \textless \ 0} \right. =\ \textgreater \ \left \{ {{x(-2; \frac{1}{7}) } \atop {x(-oo;0)}} \right. =\ \textgreater \ x (-2;0)$
отв:х∈ (-2;0)

14 votes Thanks 33

julyap

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$21 x^{2} +39x-6\ \textless \ 0 \\ x\ \textless \ 0 \\ \\ 21 x^{2} +39x-6=0|:3 \\ 7 x^{2} +13x-2=0 \\ D=169+56=225 \\ \sqrt{D} =15 \\ x_{1} = \frac{-13+15}{14} = \frac{2}{14} = \frac{1}{7} \\ x_{2} = \frac{-13-15}{14} = \frac{-28}{14} =-2 \\ \\ x\in (-2; \frac{1}{7} ) \\ x\ \textless \ 0 \\ x\in (-2;0)$

4 votes Thanks 12

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