4x^2 = 81

Question

4x^2 = 81

anonymous · Answer

In order to solve for x, we must first isolate it.$$4x^2 = 81 \implies x^2 = 81/4$$Can you solve for x from here?

@bryson

anonymous · Answer

@Luis_Rivera obviously thats why im on this site

anonymous · Answer

i need help completing the square

anonymous · Answer

x is a variable to represent an unknown value. 
To get x, you have to square-root both sides. Like this:$$x^2=16 \rightarrow \sqrt{x^2}=\pm \sqrt{16} $$$$x=\pm4$$Remember that in taking the square-root it is always positive and negative sign (for some reason i forgot) :) helps?

jim_thompson5910 · Answer

Here is one way to solve


4x^2 = 81


4x^2 - 81 = 0


(2x)^2 - (9)^2 = 0


(2x - 9)(2x + 9) = 0 ... use the difference of squares rule here


2x-9 = 0 or 2x+9 = 0


2x = 9 or 2x = -9


x = 9/2 or x = -9/2

anonymous · Answer

thanks @Lynncake & @jim_thompson5910

jim_thompson5910 · Answer

you're welcome

anonymous · Answer

you're welcome :) glad i could help