Solve for x
x = \frac{\sqrt{13} - 1}{2} \approx 1.302775638
x=\frac{-\sqrt{13}-1}{2}\approx -2.302775638
Graph
Share
Copied to clipboard
x^{2}+x+2=5
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}+x+2-5=5-5
Subtract 5 from both sides of the equation.
x^{2}+x+2-5=0
Subtracting 5 from itself leaves 0.
x^{2}+x-3=0
Subtract 5 from 2.
x=\frac{-1±\sqrt{1^{2}-4\left(-3\right)}}{2}
This equation is in standard form: ax^{2}+bx+c=0. Substitute 1 for a, 1 for b, and -3 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
x=\frac{-1±\sqrt{1-4\left(-3\right)}}{2}
Square 1.
x=\frac{-1±\sqrt{1+12}}{2}
Multiply -4 times -3.
x=\frac{-1±\sqrt{13}}{2}
Add 1 to 12.
x=\frac{\sqrt{13}-1}{2}
Now solve the equation x=\frac{-1±\sqrt{13}}{2} when ± is plus. Add -1 to \sqrt{13}.
x=\frac{-\sqrt{13}-1}{2}
Now solve the equation x=\frac{-1±\sqrt{13}}{2} when ± is minus. Subtract \sqrt{13} from -1.
x=\frac{\sqrt{13}-1}{2} x=\frac{-\sqrt{13}-1}{2}
The equation is now solved.
x^{2}+x+2=5
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}+x+2-2=5-2
Subtract 2 from both sides of the equation.
x^{2}+x=5-2
Subtracting 2 from itself leaves 0.
x^{2}+x=3
Subtract 2 from 5.
x^{2}+x+\left(\frac{1}{2}\right)^{2}=3+\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.
x^{2}+x+\frac{1}{4}=3+\frac{1}{4}
Square \frac{1}{2} by squaring both the numerator and the denominator of the fraction.
x^{2}+x+\frac{1}{4}=\frac{13}{4}
Add 3 to \frac{1}{4}.
\left(x+\frac{1}{2}\right)^{2}=\frac{13}{4}
Factor x^{2}+x+\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(x+\frac{1}{2}\right)^{2}}=\sqrt{\frac{13}{4}}
Take the square root of both sides of the equation.
x+\frac{1}{2}=\frac{\sqrt{13}}{2} x+\frac{1}{2}=-\frac{\sqrt{13}}{2}
Simplify.
x=\frac{\sqrt{13}-1}{2} x=\frac{-\sqrt{13}-1}{2}
Subtract \frac{1}{2} from 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}