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#### karush

##### Well-known member

- Jan 31, 2012

- 3,066

1183

well by completing the square from $x^2+3x$ we get $\pmatrix {x+\frac{3}{2}}^2 -\frac{9}{4}$

which means the vertex is more than $2$ below the x-axis but above at $3$

so from the set k only at $k=1$ and $k=2$ will it cross the x-axis so $\frac{2}{7}$ is the probability that the function will cross the x-axis.

one way i guess

well by completing the square from $x^2+3x$ we get $\pmatrix {x+\frac{3}{2}}^2 -\frac{9}{4}$

which means the vertex is more than $2$ below the x-axis but above at $3$

so from the set k only at $k=1$ and $k=2$ will it cross the x-axis so $\frac{2}{7}$ is the probability that the function will cross the x-axis.

one way i guess

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