Solve for a
a=\frac{1+\sqrt{3}i}{2}\approx 0.5+0.866025404i
a=\frac{-\sqrt{3}i+1}{2}\approx 0.5-0.866025404i
Share
Copied to clipboard
a^{2}-a=-1
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.
a^{2}-a-\left(-1\right)=-1-\left(-1\right)
Add 1 to both sides of the equation.
a^{2}-a-\left(-1\right)=0
Subtracting -1 from itself leaves 0.
a^{2}-a+1=0
Subtract -1 from 0.
a=\frac{-\left(-1\right)±\sqrt{1-4}}{2}
This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, -1 for b, and 1 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
a=\frac{-\left(-1\right)±\sqrt{-3}}{2}
Add 1 to -4.
a=\frac{-\left(-1\right)±\sqrt{3}i}{2}
Take the square root of -3.
a=\frac{1±\sqrt{3}i}{2}
The opposite of -1 is 1.
a=\frac{1+\sqrt{3}i}{2}
Now solve the equation a=\frac{1±\sqrt{3}i}{2} when ± is plus. Add 1 to i\sqrt{3}.
a=\frac{-\sqrt{3}i+1}{2}
Now solve the equation a=\frac{1±\sqrt{3}i}{2} when ± is minus. Subtract i\sqrt{3} from 1.
a=\frac{1+\sqrt{3}i}{2} a=\frac{-\sqrt{3}i+1}{2}
The equation is now solved.
a^{2}-a=-1
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.
a^{2}-a+\left(-\frac{1}{2}\right)^{2}=-1+\left(-\frac{1}{2}\right)^{2}
Divide -1, the coefficient of the x term, by 2 to get -\frac{1}{2}. Then add the square of -\frac{1}{2} to both sides of the equation. This step makes the left hand side of the equation a perfect square.
a^{2}-a+\frac{1}{4}=-1+\frac{1}{4}
Square -\frac{1}{2} by squaring both the numerator and the denominator of the fraction.
a^{2}-a+\frac{1}{4}=-\frac{3}{4}
Add -1 to \frac{1}{4}.
\left(a-\frac{1}{2}\right)^{2}=-\frac{3}{4}
Factor a^{2}-a+\frac{1}{4}. In general, when x^{2}+bx+c is a perfect square, it can always be factored as \left(x+\frac{b}{2}\right)^{2}.
\sqrt{\left(a-\frac{1}{2}\right)^{2}}=\sqrt{-\frac{3}{4}}
Take the square root of both sides of the equation.
a-\frac{1}{2}=\frac{\sqrt{3}i}{2} a-\frac{1}{2}=-\frac{\sqrt{3}i}{2}
Simplify.
a=\frac{1+\sqrt{3}i}{2} a=\frac{-\sqrt{3}i+1}{2}
Add \frac{1}{2} to both sides of the equation.
Examples
Quadratic equation
{ x } ^ { 2 } - 4 x - 5 = 0
Trigonometry
4 \sin \theta \cos \theta = 2 \sin \theta
Linear equation
y = 3x + 4
Arithmetic
699 * 533
Matrix
\left[ \begin{array} { l l } { 2 } & { 3 } \\ { 5 } & { 4 } \end{array} \right] \left[ \begin{array} { l l l } { 2 } & { 0 } & { 3 } \\ { -1 } & { 1 } & { 5 } \end{array} \right]
Simultaneous equation
\left. \begin{cases} { 8x+2y = 46 } \\ { 7x+3y = 47 } \end{cases} \right.
Differentiation
\frac { d } { d x } \frac { ( 3 x ^ { 2 } - 2 ) } { ( x - 5 ) }
Integration
\int _ { 0 } ^ { 1 } x e ^ { - x ^ { 2 } } d x
Limits
\lim _{x \rightarrow-3} \frac{x^{2}-9}{x^{2}+2 x-3}