How do you solve the quadratic equation 5x^2 + 3x = 1 ?

2 Answers
Aug 5, 2016

x_(1,2) = (-5 +- sqrt(13))/10

Explanation:

The first thing to do here is rearrange your equation to quadratic form by getting all the terms on one side of the equation.

To do that, subtract 1 from both sides of the equation

5x^2 + 3x - 1 = color(red)(cancel(color(black)(1))) - color(red)(cancel(color(black)(1)))

5x^2 + 3x - 1 = 0

Now, the quadratic formula allows you to calculate the two solutions of a general form quadratic equation

color(blue)(ax^2 + bx + c = 0)

by using the equation

color(blue)(|bar(ul(color(white)(a/a)x_(1,2) = (- b +- sqrt(b^2 - 4 * a * c))/(2 * a) color(white)(a/a)|)))

In your case, you have

{(a = color(white)(-)5), (b = color(white)(-)3), (c = -1) :}

Plug these values into the quadratic formula to get

x_(1,2) = (-5 +- sqrt(3^2 - 4 * 1 * (-1)))/(2 * 5)

x_(1,2) = (-5 +- sqrt(13))/10 implies {(x_1 = (-5 - sqrt(13))/10), (x_2 = (-5 + sqrt(13))/10) :}

You can thus say that your original equation has two solutions

x = (-5 - sqrt(13))/10" " and " "x = (-5 + sqrt(13))/10

graph{5x^2 + 3x - 1 [-3, 3, -3, 3]}

Aug 5, 2016

(-3 +- sqrt29)/10

Explanation:

Bring the quadratic equation to standard form:
y = 5x^2 + 3x - 1 = 0
Use the new quadratic formula in graphic form:
D = d^2 = b^2 - 4ac = 9 + 20 = 29 --> d = +- sqrt29
There are 2 real roots:
x = -b/(2a) +- d/(2a) = -3/10 +- sqrt29/10 = (-3 +- sqrt29)/10

NOTE. Using the improved quadratic formula gets simpler expressions and easier numeric computation. In addition, it shows students the graphic representation and interpretation of the axis of symmetry and the 2 x-intercepts.
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