Solve -x^2-7x+5

$$- x ^ { 2 } - 7 x + 5$$

Factor

$$-\left(x-\frac{-\sqrt{69}-7}{2}\right)\left(x-\frac{\sqrt{69}-7}{2}\right)$$

Steps Using the Quadratic Formula

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.

$$-x^{2}-7x+5=0$$

All equations of the form ax^{2}+bx+c=0 can be solved using the quadratic formula: \frac{-b±\sqrt{b^{2}-4ac}}{2a}. The quadratic formula gives two solutions, one when ± is addition and one when it is subtraction.

$$x=\frac{-\left(-7\right)±\sqrt{\left(-7\right)^{2}-4\left(-1\right)\times 5}}{2\left(-1\right)}$$

Square -7.

$$x=\frac{-\left(-7\right)±\sqrt{49-4\left(-1\right)\times 5}}{2\left(-1\right)}$$

Multiply -4 times -1.

$$x=\frac{-\left(-7\right)±\sqrt{49+4\times 5}}{2\left(-1\right)}$$

Multiply 4 times 5.

$$x=\frac{-\left(-7\right)±\sqrt{49+20}}{2\left(-1\right)}$$

Add 49 to 20.

$$x=\frac{-\left(-7\right)±\sqrt{69}}{2\left(-1\right)}$$

The opposite of -7 is 7.

$$x=\frac{7±\sqrt{69}}{2\left(-1\right)}$$

Multiply 2 times -1.

$$x=\frac{7±\sqrt{69}}{-2}$$

Now solve the equation x=\frac{7±\sqrt{69}}{-2} when ± is plus. Add 7 to \sqrt{69}.

$$x=\frac{\sqrt{69}+7}{-2}$$

Divide 7+\sqrt{69} by -2.

$$x=\frac{-\sqrt{69}-7}{2}$$

Now solve the equation x=\frac{7±\sqrt{69}}{-2} when ± is minus. Subtract \sqrt{69} from 7.

$$x=\frac{7-\sqrt{69}}{-2}$$

Divide 7-\sqrt{69} by -2.

$$x=\frac{\sqrt{69}-7}{2}$$

Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute \frac{-7-\sqrt{69}}{2} for x_{1} and \frac{-7+\sqrt{69}}{2} for x_{2}.

$$-x^{2}-7x+5=-\left(x-\frac{-\sqrt{69}-7}{2}\right)\left(x-\frac{\sqrt{69}-7}{2}\right)$$

Steps Using Direct Factoring Method

Quadratic equations such as this one can be solved by a new direct factoring method that does not require guess work. To use the direct factoring method, the equation must be in the form x^2+Bx+C=0.

$$x ^ 2 +7x -5 = 0$$

Let r and s be the factors for the quadratic equation such that x^2+Bx+C=(x−r)(x−s) where sum of factors (r+s)=−B and the product of factors rs = C

$$r + s = -7 rs = -5$$

Two numbers r and s sum up to -7 exactly when the average of the two numbers is \frac{1}{2}*-7 = -\frac{7}{2}. You can also see that the midpoint of r and s corresponds to the axis of symmetry of the parabola represented by the quadratic equation y=x^2+Bx+C. The values of r and s are equidistant from the center by an unknown quantity u. Express r and s with respect to variable u. <div style='padding: 8px'><img src='https://opalmath.azureedge.net/customsolver/quadraticgraph.png' style='width: 100%;max-width: 700px' /></div>

$$r = -\frac{7}{2} - u s = -\frac{7}{2} + u$$

To solve for unknown quantity u, substitute these in the product equation rs = -5

$$(-\frac{7}{2} - u) (-\frac{7}{2} + u) = -5$$

Simplify by expanding (a -b) (a + b) = a^2 – b^2

$$\frac{49}{4} - u^2 = -5$$

Simplify the expression by subtracting \frac{49}{4} on both sides

$$-u^2 = -5-\frac{49}{4} = -\frac{69}{4}$$

Simplify the expression by multiplying -1 on both sides and take the square root to obtain the value of unknown variable u

$$u^2 = \frac{69}{4} u = \pm\sqrt{\frac{69}{4}} = \pm \frac{\sqrt{69}}{2}$$

The factors r and s are the solutions to the quadratic equation. Substitute the value of u to compute the r and s.

$$r =-\frac{7}{2} - \frac{\sqrt{69}}{2} = -7.653 s = -\frac{7}{2} + \frac{\sqrt{69}}{2} = 0.653$$

Evaluate

$$5-7x-x^{2}$$