Solve 0.0015x^2-0.14x-30=0

$$0.0015 { x }^{ 2 } -0.14x-30 = 0$$

Solve for x

$$x = \frac{20 \sqrt{499} + 140}{3} \approx 195.588719358$$

$$x=\frac{140-20\sqrt{499}}{3}\approx -102.255386025$$

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.

$$0.0015x^{2}-0.14x-30=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute 0.0015 for a, -0.14 for b, and -30 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$x=\frac{-\left(-0.14\right)±\sqrt{\left(-0.14\right)^{2}-4\times 0.0015\left(-30\right)}}{2\times 0.0015}$$

Square -0.14 by squaring both the numerator and the denominator of the fraction.

$$x=\frac{-\left(-0.14\right)±\sqrt{0.0196-4\times 0.0015\left(-30\right)}}{2\times 0.0015}$$

Multiply -4 times 0.0015.

$$x=\frac{-\left(-0.14\right)±\sqrt{0.0196-0.006\left(-30\right)}}{2\times 0.0015}$$

Multiply -0.006 times -30.

$$x=\frac{-\left(-0.14\right)±\sqrt{0.0196+0.18}}{2\times 0.0015}$$

Add 0.0196 to 0.18 by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$x=\frac{-\left(-0.14\right)±\sqrt{0.1996}}{2\times 0.0015}$$

Take the square root of 0.1996.

$$x=\frac{-\left(-0.14\right)±\frac{\sqrt{499}}{50}}{2\times 0.0015}$$

The opposite of -0.14 is 0.14.

$$x=\frac{0.14±\frac{\sqrt{499}}{50}}{2\times 0.0015}$$

Multiply 2 times 0.0015.

$$x=\frac{0.14±\frac{\sqrt{499}}{50}}{0.003}$$

Now solve the equation x=\frac{0.14±\frac{\sqrt{499}}{50}}{0.003} when ± is plus. Add 0.14 to \frac{\sqrt{499}}{50}.

$$x=\frac{\sqrt{499}+7}{0.003\times 50}$$

Divide \frac{7+\sqrt{499}}{50} by 0.003 by multiplying \frac{7+\sqrt{499}}{50} by the reciprocal of 0.003.

$$x=\frac{20\sqrt{499}+140}{3}$$

Now solve the equation x=\frac{0.14±\frac{\sqrt{499}}{50}}{0.003} when ± is minus. Subtract \frac{\sqrt{499}}{50} from 0.14.

$$x=\frac{7-\sqrt{499}}{0.003\times 50}$$

Divide \frac{7-\sqrt{499}}{50} by 0.003 by multiplying \frac{7-\sqrt{499}}{50} by the reciprocal of 0.003.

$$x=\frac{140-20\sqrt{499}}{3}$$

The equation is now solved.

$$x=\frac{20\sqrt{499}+140}{3} x=\frac{140-20\sqrt{499}}{3}$$

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.

$$0.0015x^{2}-0.14x-30=0$$

Add 30 to both sides of the equation.

$$0.0015x^{2}-0.14x-30-\left(-30\right)=-\left(-30\right)$$

Subtracting -30 from itself leaves 0.

$$0.0015x^{2}-0.14x=-\left(-30\right)$$

Subtract -30 from 0.

$$0.0015x^{2}-0.14x=30$$

Divide both sides of the equation by 0.0015, which is the same as multiplying both sides by the reciprocal of the fraction.

$$\frac{0.0015x^{2}-0.14x}{0.0015}=\frac{30}{0.0015}$$

Dividing by 0.0015 undoes the multiplication by 0.0015.

$$x^{2}+\left(-\frac{0.14}{0.0015}\right)x=\frac{30}{0.0015}$$

Divide -0.14 by 0.0015 by multiplying -0.14 by the reciprocal of 0.0015.

$$x^{2}-\frac{280}{3}x=\frac{30}{0.0015}$$

Divide 30 by 0.0015 by multiplying 30 by the reciprocal of 0.0015.

$$x^{2}-\frac{280}{3}x=20000$$

Divide -\frac{280}{3}, the coefficient of the x term, by 2 to get -\frac{140}{3}. Then add the square of -\frac{140}{3} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$x^{2}-\frac{280}{3}x+\left(-\frac{140}{3}\right)^{2}=20000+\left(-\frac{140}{3}\right)^{2}$$

Square -\frac{140}{3} by squaring both the numerator and the denominator of the fraction.

$$x^{2}-\frac{280}{3}x+\frac{19600}{9}=20000+\frac{19600}{9}$$

Add 20000 to \frac{19600}{9}.

$$x^{2}-\frac{280}{3}x+\frac{19600}{9}=\frac{199600}{9}$$

Factor x^{2}-\frac{280}{3}x+\frac{19600}{9}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(x-\frac{140}{3}\right)^{2}=\frac{199600}{9}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(x-\frac{140}{3}\right)^{2}}=\sqrt{\frac{199600}{9}}$$

Simplify.

$$x-\frac{140}{3}=\frac{20\sqrt{499}}{3} x-\frac{140}{3}=-\frac{20\sqrt{499}}{3}$$

Add \frac{140}{3} to both sides of the equation.

$$x=\frac{20\sqrt{499}+140}{3} x=\frac{140-20\sqrt{499}}{3}$$