Solve 2x^2+15x+36

$$2 x ^ { 2 } + 15 x + 36$$

Evaluate

$$2x^{2}+15x+36$$

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 2

$$x ^ 2 +\frac{15}{2}x +18 = 0$$

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

$$r + s = -\frac{15}{2} rs = 18$$

Two numbers r and s sum up to -\frac{15}{2} exactly when the average of the two numbers is \frac{1}{2}*-\frac{15}{2} = -\frac{15}{4}. 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>

$$r = -\frac{15}{4} - u s = -\frac{15}{4} + u$$

To solve for unknown quantity u, substitute these in the product equation rs = 18

$$(-\frac{15}{4} - u) (-\frac{15}{4} + u) = 18$$

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

$$\frac{225}{16} - u^2 = 18$$

Simplify the expression by subtracting \frac{225}{16} on both sides

$$-u^2 = 18-\frac{225}{16} = \frac{63}{16}$$

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

$$u^2 = -\frac{63}{16} u = \pm\sqrt{-\frac{63}{16}} = \pm \frac{\sqrt{63}}{4}i$$

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

$$r =-\frac{15}{4} - \frac{\sqrt{63}}{4}i = -3.750 - 1.984i s = -\frac{15}{4} + \frac{\sqrt{63}}{4}i = -3.750 + 1.984i$$

Differentiate w.r.t. x

$$4x+15$$

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}.

$$2\times 2x^{2-1}+15x^{1-1}$$

Multiply 2 times 2.

$$4x^{2-1}+15x^{1-1}$$

Subtract 1 from 2.

$$4x^{1}+15x^{1-1}$$

Subtract 1 from 1.

$$4x^{1}+15x^{0}$$

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

$$4x+15x^{0}$$

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

$$4x+15\times 1$$

For any term t, t\times 1=t and 1t=t.

$$4x+15$$