3xsquared - 21=0 solve for x?

3x^2 - 21 = 0
3x^2 = 21
x^2 = 7
x = sqrt(7)

3x^2 - 21 = 0

First you need to move -21 to the other side of = but remember when moving you have to change sign to positive

3x^2 = 21

Then you need to get 3 away from the x in order to do that 3 needs to be divided be 21 since 3 and x are being multiplied

x^2 = 21/3

x^2 = 7

Transpose -21 to the other side that's why it is now +21.
Divide both sides by 3, leaving x^2=7.
Square both sides resulting to x=sqrt7.

3x^2 - 21 = 0
3x^2 = 21
x^2 = 21/2
x^2 = 7
x = ±√7

3 x ² = 21
x ² = 7
x = ± √7

Factor out the 3

3(x^2 - 7) = 0

x^2 - 7 = 0

x^2 = 7

x = sqrt(7) x = -sqrt(7)

3x^2-21=0
x^2-7=0
x=square root of 7 and -square root 7

3x²-21 = 0

3x² = 21

x² = 7

x = ±√7 ≈ ± 2.646