Solve 5x^2+4x-1>0

$$5 x ^ { 2 } + 4 x - 1 > 0$$

Solve for x

$$x\in \left(-\infty,-1\right)\cup \left(\frac{1}{5},\infty\right)$$

Steps Using the Quadratic Formula

To solve the inequality, factor the left hand side. Quadratic polynomial can be factored using the transformation ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right), where x_{1} and x_{2} are the solutions of the quadratic equation ax^{2}+bx+c=0.

$$5x^{2}+4x-1=0$$

All equations of the form ax^{2}+bx+c=0 can be solved using the quadratic formula: \frac{-b±\sqrt{b^{2}-4ac}}{2a}. Substitute 5 for a, 4 for b, and -1 for c in the quadratic formula.

$$x=\frac{-4±\sqrt{4^{2}-4\times 5\left(-1\right)}}{2\times 5}$$

Do the calculations.

$$x=\frac{-4±6}{10}$$

Solve the equation x=\frac{-4±6}{10} when ± is plus and when ± is minus.

$$x=\frac{1}{5} x=-1$$

Rewrite the inequality by using the obtained solutions.

$$5\left(x-\frac{1}{5}\right)\left(x+1\right)>0$$

For the product to be positive, x-\frac{1}{5} and x+1 have to be both negative or both positive. Consider the case when x-\frac{1}{5} and x+1 are both negative.

$$x-\frac{1}{5}<0 x+1<0$$

The solution satisfying both inequalities is x<-1.

$$x<-1$$

Consider the case when x-\frac{1}{5} and x+1 are both positive.

$$x+1>0 x-\frac{1}{5}>0$$

The solution satisfying both inequalities is x>\frac{1}{5}.

$$x>\frac{1}{5}$$

The final solution is the union of the obtained solutions.

$$x<-1\text{; }x>\frac{1}{5}$$