Solve 3x^2-2x+18

$$3 x ^ { 2 } - 2 x + 18$$

Evaluate

$$3x^{2}-2x+18$$

Steps Using Direct Factoring Method

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.This is achieved by dividing both sides of the equation by 3

$$x ^ 2 -\frac{2}{3}x +6 = 0$$

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

$$r + s = \frac{2}{3} rs = 6$$

Two numbers r and s sum up to \frac{2}{3} exactly when the average of the two numbers is \frac{1}{2}*\frac{2}{3} = \frac{1}{3}. 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>

$$r = \frac{1}{3} - u s = \frac{1}{3} + u$$

To solve for unknown quantity u, substitute these in the product equation rs = 6

$$(\frac{1}{3} - u) (\frac{1}{3} + u) = 6$$

Simplify by expanding (a -b) (a + b) = a^2 – b^2

$$\frac{1}{9} - u^2 = 6$$

Simplify the expression by subtracting \frac{1}{9} on both sides

$$-u^2 = 6-\frac{1}{9} = \frac{53}{9}$$

Simplify the expression by multiplying -1 on both sides and take the square root to obtain the value of unknown variable u

$$u^2 = -\frac{53}{9} u = \pm\sqrt{-\frac{53}{9}} = \pm \frac{\sqrt{53}}{3}i$$

The factors r and s are the solutions to the quadratic equation. Substitute the value of u to compute the r and s.

$$r =\frac{1}{3} - \frac{\sqrt{53}}{3}i = 0.333 - 2.427i s = \frac{1}{3} + \frac{\sqrt{53}}{3}i = 0.333 + 2.427i$$

Differentiate w.r.t. x

$$6x-2$$

Steps Using Derivative Rule for Sum

The derivative of a polynomial is the sum of the derivatives of its terms. The derivative of a constant term is 0. The derivative of ax^{n} is nax^{n-1}.

$$2\times 3x^{2-1}-2x^{1-1}$$

Multiply 2 times 3.

$$6x^{2-1}-2x^{1-1}$$

Subtract 1 from 2.

$$6x^{1}-2x^{1-1}$$

Subtract 1 from 1.

$$6x^{1}-2x^{0}$$

For any term t, t^{1}=t.

$$6x-2x^{0}$$

For any term t except 0, t^{0}=1.

$$6x-2$$