Solve for x
x=-6
x=7
Graph
Share
Copied to clipboard
52-x^{2}+x-10=0
Subtract 10 from both sides.
42-x^{2}+x=0
Subtract 10 from 52 to get 42.
-x^{2}+x+42=0
Rearrange the polynomial to put it in standard form. Place the terms in order from highest to lowest power.
a+b=1 ab=-42=-42
To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as -x^{2}+ax+bx+42. To find a and b, set up a system to be solved.
-1,42 -2,21 -3,14 -6,7
Since ab is negative, a and b have the opposite signs. Since a+b is positive, the positive number has greater absolute value than the negative. List all such integer pairs that give product -42.
-1+42=41 -2+21=19 -3+14=11 -6+7=1
Calculate the sum for each pair.
a=7 b=-6
The solution is the pair that gives sum 1.
\left(-x^{2}+7x\right)+\left(-6x+42\right)
Rewrite -x^{2}+x+42 as \left(-x^{2}+7x\right)+\left(-6x+42\right).
-x\left(x-7\right)-6\left(x-7\right)
Factor out -x in the first and -6 in the second group.
\left(x-7\right)\left(-x-6\right)
Factor out common term x-7 by using distributive property.
x=7 x=-6
To find equation solutions, solve x-7=0 and -x-6=0.
-x^{2}+x+52=10
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+52-10=10-10
Subtract 10 from both sides of the equation.
-x^{2}+x+52-10=0
Subtracting 10 from itself leaves 0.
-x^{2}+x+42=0
Subtract 10 from 52.
x=\frac{-1±\sqrt{1^{2}-4\left(-1\right)\times 42}}{2\left(-1\right)}
This equation is in standard form: ax^{2}+bx+c=0. Substitute -1 for a, 1 for b, and 42 for c in the quadratic formula, \frac{-b±\sqrt{b^{2}-4ac}}{2a}.
x=\frac{-1±\sqrt{1-4\left(-1\right)\times 42}}{2\left(-1\right)}
Square 1.
x=\frac{-1±\sqrt{1+4\times 42}}{2\left(-1\right)}
Multiply -4 times -1.
x=\frac{-1±\sqrt{1+168}}{2\left(-1\right)}
Multiply 4 times 42.
x=\frac{-1±\sqrt{169}}{2\left(-1\right)}
Add 1 to 168.
x=\frac{-1±13}{2\left(-1\right)}
Take the square root of 169.
x=\frac{-1±13}{-2}
Multiply 2 times -1.
x=\frac{12}{-2}
Now solve the equation x=\frac{-1±13}{-2} when ± is plus. Add -1 to 13.
x=-6
Divide 12 by -2.
x=-\frac{14}{-2}
Now solve the equation x=\frac{-1±13}{-2} when ± is minus. Subtract 13 from -1.
x=7
Divide -14 by -2.
x=-6 x=7
The equation is now solved.
-x^{2}+x+52=10
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+52-52=10-52
Subtract 52 from both sides of the equation.
-x^{2}+x=10-52
Subtracting 52 from itself leaves 0.
-x^{2}+x=-42
Subtract 52 from 10.
\frac{-x^{2}+x}{-1}=-\frac{42}{-1}
Divide both sides by -1.
x^{2}+\frac{1}{-1}x=-\frac{42}{-1}
Dividing by -1 undoes the multiplication by -1.
x^{2}-x=-\frac{42}{-1}
Divide 1 by -1.
x^{2}-x=42
Divide -42 by -1.
x^{2}-x+\left(-\frac{1}{2}\right)^{2}=42+\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}=42+\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{169}{4}
Add 42 to \frac{1}{4}.
\left(x-\frac{1}{2}\right)^{2}=\frac{169}{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{169}{4}}
Take the square root of both sides of the equation.
x-\frac{1}{2}=\frac{13}{2} x-\frac{1}{2}=-\frac{13}{2}
Simplify.
x=7 x=-6
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}