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a+b=4 ab=1\left(-12\right)=-12
Factor the expression by grouping. First, the expression needs to be rewritten as k^{2}+ak+bk-12. To find a and b, set up a system to be solved.
-1,12 -2,6 -3,4
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 -12.
-1+12=11 -2+6=4 -3+4=1
Calculate the sum for each pair.
a=-2 b=6
The solution is the pair that gives sum 4.
\left(k^{2}-2k\right)+\left(6k-12\right)
Rewrite k^{2}+4k-12 as \left(k^{2}-2k\right)+\left(6k-12\right).
k\left(k-2\right)+6\left(k-2\right)
Factor out k in the first and 6 in the second group.
\left(k-2\right)\left(k+6\right)
Factor out common term k-2 by using distributive property.
k^{2}+4k-12=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.
k=\frac{-4±\sqrt{4^{2}-4\left(-12\right)}}{2}
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.
k=\frac{-4±\sqrt{16-4\left(-12\right)}}{2}
Square 4.
k=\frac{-4±\sqrt{16+48}}{2}
Multiply -4 times -12.
k=\frac{-4±\sqrt{64}}{2}
Add 16 to 48.
k=\frac{-4±8}{2}
Take the square root of 64.
k=\frac{4}{2}
Now solve the equation k=\frac{-4±8}{2} when ± is plus. Add -4 to 8.
k=2
Divide 4 by 2.
k=-\frac{12}{2}
Now solve the equation k=\frac{-4±8}{2} when ± is minus. Subtract 8 from -4.
k=-6
Divide -12 by 2.
k^{2}+4k-12=\left(k-2\right)\left(k-\left(-6\right)\right)
Factor the original expression using ax^{2}+bx+c=a\left(x-x_{1}\right)\left(x-x_{2}\right). Substitute 2 for x_{1} and -6 for x_{2}.
k^{2}+4k-12=\left(k-2\right)\left(k+6\right)
Simplify all the expressions of the form p-\left(-q\right) to p+q.
x ^ 2 +4x -12 = 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 = -4 rs = -12
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 = -2 - u s = -2 + u
Two numbers r and s sum up to -4 exactly when the average of the two numbers is \frac{1}{2}*-4 = -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>
(-2 - u) (-2 + u) = -12
To solve for unknown quantity u, substitute these in the product equation rs = -12
4 - u^2 = -12
Simplify by expanding (a -b) (a + b) = a^2 – b^2
-u^2 = -12-4 = -16
Simplify the expression by subtracting 4 on both sides
u^2 = 16 u = \pm\sqrt{16} = \pm 4
Simplify the expression by multiplying -1 on both sides and take the square root to obtain the value of unknown variable u
r =-2 - 4 = -6 s = -2 + 4 = 2
The factors r and s are the solutions to the quadratic equation. Substitute the value of u to compute the r and s.