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x^2-8x+15=0

x^2-8x+15=0 equation

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Numerical solution:

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The solution

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 2               
x  - 8*x + 15 = 0
$$\left(x^{2} - 8 x\right) + 15 = 0$$
Simplify
Detail solution
This equation is of the form
a*x^2 + b*x + c = 0

A quadratic equation can be solved
using the discriminant.
The roots of the quadratic equation:
$$x_{1} = \frac{\sqrt{D} - b}{2 a}$$
$$x_{2} = \frac{- \sqrt{D} - b}{2 a}$$
where D = b^2 - 4*a*c - it is the discriminant.
Because
$$a = 1$$
$$b = -8$$
$$c = 15$$
, then
D = b^2 - 4 * a * c = 

(-8)^2 - 4 * (1) * (15) = 4

Because D > 0, then the equation has two roots.
x1 = (-b + sqrt(D)) / (2*a)

x2 = (-b - sqrt(D)) / (2*a)

or
$$x_{1} = 5$$
$$x_{2} = 3$$
Vieta's Theorem
it is reduced quadratic equation
$$p x + q + x^{2} = 0$$
where
$$p = \frac{b}{a}$$
$$p = -8$$
$$q = \frac{c}{a}$$
$$q = 15$$
Vieta Formulas
$$x_{1} + x_{2} = - p$$
$$x_{1} x_{2} = q$$
$$x_{1} + x_{2} = 8$$
$$x_{1} x_{2} = 15$$
The graph
Plot the graph f1(x)
Plot the graph f2(x)
Rapid solution [src] 
x1 = 3
$$x_{1} = 3$$ 
x2 = 5
$$x_{2} = 5$$ 
x2 = 5
Sum and product of roots [src] 
sum
3 + 5
$$3 + 5$$ 
=
8
$$8$$ 
product
3*5
$$3 \cdot 5$$ 
=
15
$$15$$ 
15
Numerical answer [src] 
x1 = 5.0
x2 = 3.0
x2 = 3.0
The graph
x^2-8x+15=0 equation
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