Question

Use any method to solve the equation. If necessary, round to the nearest hundredth.

9x2  − 21 = 0



4.58, –4.58


3, –3


0.65, –0.65


1.53, –1.53

Answer 1

`x_(1)=1.53\\x_(2)=-1.53`

Explanation:

The given quadratic equation is

`9x^(2)-21=0`

To solve this equation, we just have to isolate the variable, because the quadratic expression has only one variable, the linear term is not present. So

`9x^(2) =21\\x^(2) =(21)/(9)`

Now, we apply a square root, to have the variable complete isolated

`\sqrt{x^(2) }=\sqrt{(21)/(9) } \\x=\±1.53`

Remember that all square roots have two results, one positive and one negative.

Therefore, the solutions for this equation are

`x_(1)=1.53\\x_(2)=-1.53`

Answer 2

we have that
9x² − 21 = 0

using a graph tool
see the attached figure

the solution is
x=-1.528----> -1.53
x=1.528----> 1.53