How do you solve 3-4x^2=-85?

2 Answers
Lumpy D. ยท Stefan V.
May 8, 2018

+-sqrt(22)

Explanation:

Subtract 3 to the other side

-4x^2 = -88

Then, divide both sides by -4

x^2 = 22

Finally, take the square root of both sides.

x = +-sqrt(22)

Ben
May 8, 2018

Rearrange the expression and you will find that x=+-4.69

Explanation:

First, we'll rearrange the expression such that all of the constants are on one side of the expression, and all of the terms directly related to x are on the other side:

cancel(3)-4x^2color(red)(cancel(-3))=-85color(red)(-3)

-4x^2=-88

Now, we'll divide by the coefficient on x's side:

(cancel(-4)x^2)/color(red)(cancel(-4))=(cancel(-)88)/color(red)(cancel(-)4)

x^2=22

Finally, we'll take the square root of both sides to get the answer:

sqrt(x^2)=sqrt(22)

color(green)(x=+-sqrt(22)=+-4.69

You have to put the +- in because both positive and negative values yield positive answers when squared.

Related questions
See all questions in Use Square Roots to Solve Quadratic Equations
Impact of this question
3847 views around the world
You can reuse this answer
Creative Commons License