Solve -11a^2-35a+10.8=0

$$- 11 a ^ { 2 } - 35 a + 10.8 = 0$$

Solve for a

$$a=\frac{\sqrt{42505}}{110}-\frac{35}{22}\approx 0.28334007$$

$$a=-\frac{\sqrt{42505}}{110}-\frac{35}{22}\approx -3.465158252$$

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.

$$-11a^{2}-35a+10.8=0$$

This equation is in standard form: ax^{2}+bx+c=0. Substitute -11 for a, -35 for b, and 10.8 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.

$$a=\frac{-\left(-35\right)±\sqrt{\left(-35\right)^{2}-4\left(-11\right)\times 10.8}}{2\left(-11\right)}$$

Square -35.

$$a=\frac{-\left(-35\right)±\sqrt{1225-4\left(-11\right)\times 10.8}}{2\left(-11\right)}$$

Multiply -4 times -11.

$$a=\frac{-\left(-35\right)±\sqrt{1225+44\times 10.8}}{2\left(-11\right)}$$

Multiply 44 times 10.8.

$$a=\frac{-\left(-35\right)±\sqrt{1225+475.2}}{2\left(-11\right)}$$

Add 1225 to 475.2.

$$a=\frac{-\left(-35\right)±\sqrt{1700.2}}{2\left(-11\right)}$$

Take the square root of 1700.2.

$$a=\frac{-\left(-35\right)±\frac{\sqrt{42505}}{5}}{2\left(-11\right)}$$

The opposite of -35 is 35.

$$a=\frac{35±\frac{\sqrt{42505}}{5}}{2\left(-11\right)}$$

Multiply 2 times -11.

$$a=\frac{35±\frac{\sqrt{42505}}{5}}{-22}$$

Now solve the equation a=\frac{35±\frac{\sqrt{42505}}{5}}{-22} when ± is plus. Add 35 to \frac{\sqrt{42505}}{5}.

$$a=\frac{\frac{\sqrt{42505}}{5}+35}{-22}$$

Divide 35+\frac{\sqrt{42505}}{5} by -22.

$$a=-\frac{\sqrt{42505}}{110}-\frac{35}{22}$$

Now solve the equation a=\frac{35±\frac{\sqrt{42505}}{5}}{-22} when ± is minus. Subtract \frac{\sqrt{42505}}{5} from 35.

$$a=\frac{-\frac{\sqrt{42505}}{5}+35}{-22}$$

Divide 35-\frac{\sqrt{42505}}{5} by -22.

$$a=\frac{\sqrt{42505}}{110}-\frac{35}{22}$$

The equation is now solved.

$$a=-\frac{\sqrt{42505}}{110}-\frac{35}{22} a=\frac{\sqrt{42505}}{110}-\frac{35}{22}$$

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.

$$-11a^{2}-35a+10.8=0$$

Subtract 10.8 from both sides of the equation.

$$-11a^{2}-35a+10.8-10.8=-10.8$$

Subtracting 10.8 from itself leaves 0.

$$-11a^{2}-35a=-10.8$$

Divide both sides by -11.

$$\frac{-11a^{2}-35a}{-11}=-\frac{10.8}{-11}$$

Dividing by -11 undoes the multiplication by -11.

$$a^{2}+\left(-\frac{35}{-11}\right)a=-\frac{10.8}{-11}$$

Divide -35 by -11.

$$a^{2}+\frac{35}{11}a=-\frac{10.8}{-11}$$

Divide -10.8 by -11.

$$a^{2}+\frac{35}{11}a=\frac{54}{55}$$

Divide \frac{35}{11}, the coefficient of the x term, by 2 to get \frac{35}{22}. Then add the square of \frac{35}{22} to both sides of the equation. This step makes the left hand side of the equation a perfect square.

$$a^{2}+\frac{35}{11}a+\left(\frac{35}{22}\right)^{2}=\frac{54}{55}+\left(\frac{35}{22}\right)^{2}$$

Square \frac{35}{22} by squaring both the numerator and the denominator of the fraction.

$$a^{2}+\frac{35}{11}a+\frac{1225}{484}=\frac{54}{55}+\frac{1225}{484}$$

Add \frac{54}{55} to \frac{1225}{484} by finding a common denominator and adding the numerators. Then reduce the fraction to lowest terms if possible.

$$a^{2}+\frac{35}{11}a+\frac{1225}{484}=\frac{8501}{2420}$$

Factor a^{2}+\frac{35}{11}a+\frac{1225}{484}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.

$$\left(a+\frac{35}{22}\right)^{2}=\frac{8501}{2420}$$

Take the square root of both sides of the equation.

$$\sqrt{\left(a+\frac{35}{22}\right)^{2}}=\sqrt{\frac{8501}{2420}}$$

Simplify.

$$a+\frac{35}{22}=\frac{\sqrt{42505}}{110} a+\frac{35}{22}=-\frac{\sqrt{42505}}{110}$$

Subtract \frac{35}{22} from both sides of the equation.

$$a=\frac{\sqrt{42505}}{110}-\frac{35}{22} a=-\frac{\sqrt{42505}}{110}-\frac{35}{22}$$