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2\left(-x^{2}+x+2\right)
Factor out 2.
a+b=1 ab=-2=-2
Consider -x^{2}+x+2. Factor the expression by grouping. First, the expression needs to be rewritten as -x^{2}+ax+bx+2. To find a and b, set up a system to be solved.
a=2 b=-1
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. The only such pair is the system solution.
\left(-x^{2}+2x\right)+\left(-x+2\right)
Rewrite -x^{2}+x+2 as \left(-x^{2}+2x\right)+\left(-x+2\right).
-x\left(x-2\right)-\left(x-2\right)
Factor out -x in the first and -1 in the second group.
\left(x-2\right)\left(-x-1\right)
Factor out common term x-2 by using distributive property.
2\left(x-2\right)\left(-x-1\right)
Rewrite the complete factored expression.
-2x^{2}+2x+4=0
Quadratic polynomial can be factored using the transformation ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right), where x_{1} and x_{2} are the solutions of the quadratic equation ax^{2}+bx+c=0.
x=\frac{-2±\sqrt{2^{2}-4\left(-2\right)\times 4}}{2\left(-2\right)}
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=\frac{-2±\sqrt{4-4\left(-2\right)\times 4}}{2\left(-2\right)}
Square 2.
x=\frac{-2±\sqrt{4+8\times 4}}{2\left(-2\right)}
Multiply -4 times -2.
x=\frac{-2±\sqrt{4+32}}{2\left(-2\right)}
Multiply 8 times 4.
x=\frac{-2±\sqrt{36}}{2\left(-2\right)}
Add 4 to 32.
x=\frac{-2±6}{2\left(-2\right)}
Take the square root of 36.
x=\frac{-2±6}{-4}
Multiply 2 times -2.
x=\frac{4}{-4}
Now solve the equation x=\frac{-2±6}{-4} when ± is plus. Add -2 to 6.
x=-1
Divide 4 by -4.
x=-\frac{8}{-4}
Now solve the equation x=\frac{-2±6}{-4} when ± is minus. Subtract 6 from -2.
x=2
Divide -8 by -4.
-2x^{2}+2x+4=-2\left(x-\left(-1\right)\right)\left(x-2\right)
Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute -1 for x_{1} and 2 for x_{2}.
-2x^{2}+2x+4=-2\left(x+1\right)\left(x-2\right)
Simplify all the expressions of the form p-\left(-q\right) to p+q.
x ^ 2 -1x -2 = 0
Quadratic equations such as this one can be solved by a new direct factoring method that does not require guess work. To use the direct factoring method, the equation must be in the form x^2+Bx+C=0.
r + s = 1 rs = -2
Let r and s be the factors for the quadratic equation such that x^2+Bx+C=(x−r)(x−s) where sum of factors (r+s)=−B and the product of factors rs = C
r = \frac{1}{2} - u s = \frac{1}{2} + u
Two numbers r and s sum up to 1 exactly when the average of the two numbers is \frac{1}{2}*1 = \frac{1}{2}. You can also see that the midpoint of r and s corresponds to the axis of symmetry of the parabola represented by the quadratic equation y=x^2+Bx+C. The values of r and s are equidistant from the center by an unknown quantity u. Express r and s with respect to variable u. <div style='padding: 8px'><img src='https://opalmath.azureedge.net/customsolver/quadraticgraph.png' style='width: 100%;max-width: 700px' /></div>
(\frac{1}{2} - u) (\frac{1}{2} + u) = -2
To solve for unknown quantity u, substitute these in the product equation rs = -2
\frac{1}{4} - u^2 = -2
Simplify by expanding (a -b) (a + b) = a^2 – b^2
-u^2 = -2-\frac{1}{4} = -\frac{9}{4}
Simplify the expression by subtracting \frac{1}{4} on both sides
u^2 = \frac{9}{4} u = \pm\sqrt{\frac{9}{4}} = \pm \frac{3}{2}
Simplify the expression by multiplying -1 on both sides and take the square root to obtain the value of unknown variable u
r =\frac{1}{2} - \frac{3}{2} = -1 s = \frac{1}{2} + \frac{3}{2} = 2
The factors r and s are the solutions to the quadratic equation. Substitute the value of u to compute the r and s.