Solve 10t^2+7t+80

$$10 t ^ { 2 } + 7 t + 80$$

Evaluate

$$10t^{2}+7t+80$$

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 10

$$x ^ 2 +\frac{7}{10}x +8 = 0$$

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

$$r + s = -\frac{7}{10} rs = 8$$

Two numbers r and s sum up to -\frac{7}{10} exactly when the average of the two numbers is \frac{1}{2}*-\frac{7}{10} = -\frac{7}{20}. 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>

$$r = -\frac{7}{20} - u s = -\frac{7}{20} + u$$

To solve for unknown quantity u, substitute these in the product equation rs = 8

$$(-\frac{7}{20} - u) (-\frac{7}{20} + u) = 8$$

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

$$\frac{49}{400} - u^2 = 8$$

Simplify the expression by subtracting \frac{49}{400} on both sides

$$-u^2 = 8-\frac{49}{400} = \frac{3151}{400}$$

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

$$u^2 = -\frac{3151}{400} u = \pm\sqrt{-\frac{3151}{400}} = \pm \frac{\sqrt{3151}}{20}i$$

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

$$r =-\frac{7}{20} - \frac{\sqrt{3151}}{20}i = -0.350 - 2.807i s = -\frac{7}{20} + \frac{\sqrt{3151}}{20}i = -0.350 + 2.807i$$

Differentiate w.r.t. t

$$20t+7$$

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}.

$$2\times 10t^{2-1}+7t^{1-1}$$

Multiply 2 times 10.

$$20t^{2-1}+7t^{1-1}$$

Subtract 1 from 2.

$$20t^{1}+7t^{1-1}$$

Subtract 1 from 1.

$$20t^{1}+7t^{0}$$

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

$$20t+7t^{0}$$

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

$$20t+7\times 1$$

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

$$20t+7$$