81=4a^2

Solution for 81=4a^2 equation:

Simplifying
81 = 4a2

Solving
81 = 4a2

Solving for variable 'a'.

Move all terms containing a to the left, all other terms to the right.

Add '-4a2' to each side of the equation.
81 + -4a2 = 4a2 + -4a2

Combine like terms: 4a2 + -4a2 = 0
81 + -4a2 = 0

Add '-81' to each side of the equation.
81 + -81 + -4a2 = 0 + -81

Combine like terms: 81 + -81 = 0
0 + -4a2 = 0 + -81
-4a2 = 0 + -81

Combine like terms: 0 + -81 = -81
-4a2 = -81

Divide each side by '-4'.
a2 = 20.25

Simplifying
a2 = 20.25

Take the square root of each side:
a = {-4.5, 4.5}