R^2-4-21=0

Solution for R^2-4-21=0 equation:

Simplifying
R2 + -4 + -21 = 0

Reorder the terms:
-4 + -21 + R2 = 0

Combine like terms: -4 + -21 = -25
-25 + R2 = 0

Solving
-25 + R2 = 0

Solving for variable 'R'.

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

Add '25' to each side of the equation.
-25 + 25 + R2 = 0 + 25

Combine like terms: -25 + 25 = 0
0 + R2 = 0 + 25
R2 = 0 + 25

Combine like terms: 0 + 25 = 25
R2 = 25

Simplifying
R2 = 25

Take the square root of each side:
R = {-5, 5}