Solve x^2+3200x-180000=0

$$x ^ { 2 } + 3200 x - 180000 = 0$$

Solve for x

$$x=100\sqrt{274}-1600\approx 55.294535725$$

$$x=-100\sqrt{274}-1600\approx -3255.294535725$$

Steps Using the Quadratic Formula

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.

$$x^{2}+3200x-180000=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, 3200 for b, and -180000 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-3200±\sqrt{3200^{2}-4\left(-180000\right)}}{2}$$

Square 3200.

$$x=\frac{-3200±\sqrt{10240000-4\left(-180000\right)}}{2}$$

Multiply -4 times -180000.

$$x=\frac{-3200±\sqrt{10240000+720000}}{2}$$

Add 10240000 to 720000.

$$x=\frac{-3200±\sqrt{10960000}}{2}$$

Take the square root of 10960000.

$$x=\frac{-3200±200\sqrt{274}}{2}$$

Now solve the equation x=\frac{-3200±200\sqrt{274}}{2} when ± is plus. Add -3200 to 200\sqrt{274}.

$$x=\frac{200\sqrt{274}-3200}{2}$$

Divide -3200+200\sqrt{274} by 2.

$$x=100\sqrt{274}-1600$$

Now solve the equation x=\frac{-3200±200\sqrt{274}}{2} when ± is minus. Subtract 200\sqrt{274} from -3200.

$$x=\frac{-200\sqrt{274}-3200}{2}$$

Divide -3200-200\sqrt{274} by 2.

$$x=-100\sqrt{274}-1600$$

The equation is now solved.

$$x=100\sqrt{274}-1600 x=-100\sqrt{274}-1600$$

Steps for Completing the Square

Quadratic equations such as this one can be solved by completing the square. In order to complete the square, the equation must first be in the form x^{2}+bx=c.

$$x^{2}+3200x-180000=0$$

Add 180000 to both sides of the equation.

$$x^{2}+3200x-180000-\left(-180000\right)=-\left(-180000\right)$$

Subtracting -180000 from itself leaves 0.

$$x^{2}+3200x=-\left(-180000\right)$$

Subtract -180000 from 0.

$$x^{2}+3200x=180000$$

Divide 3200, the coefficient of the x term, by 2 to get 1600. Then add the square of 1600 to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}+3200x+1600^{2}=180000+1600^{2}$$

Square 1600.

$$x^{2}+3200x+2560000=180000+2560000$$

Add 180000 to 2560000.

$$x^{2}+3200x+2560000=2740000$$

Factor x^{2}+3200x+2560000. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x+1600\right)^{2}=2740000$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x+1600\right)^{2}}=\sqrt{2740000}$$

Simplify.

$$x+1600=100\sqrt{274} x+1600=-100\sqrt{274}$$

Subtract 1600 from both sides of the equation.

$$x=100\sqrt{274}-1600 x=-100\sqrt{274}-1600$$

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.

$$x ^ 2 +3200x -180000 = 0$$

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

$$r + s = -3200 rs = -180000$$

Two numbers r and s sum up to -3200 exactly when the average of the two numbers is \frac{1}{2}*-3200 = -1600. 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>

$$r = -1600 - u s = -1600 + u$$

To solve for unknown quantity u, substitute these in the product equation rs = -180000

$$(-1600 - u) (-1600 + u) = -180000$$

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

$$2560000 - u^2 = -180000$$

Simplify the expression by subtracting 2560000 on both sides

$$-u^2 = -180000-2560000 = -2740000$$

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

$$u^2 = 2740000 u = \pm\sqrt{2740000} = \pm \sqrt{2740000}$$

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

$$r =-1600 - \sqrt{2740000} = -3255.295 s = -1600 + \sqrt{2740000} = 55.295$$