T=2pi√I/g. find I
T = 2 π √ ( I / g )
Square both sides of the equation
T² = ( 2 π )² ∙ [ √ ( I / g ) ]²
T² = 4 π ² ∙ I / g
Multiply both sides by g
T² ∙ g = 4 π ² ∙ I
Divide both sides by 4 π ²
T² ∙ g / 4 π ² = I
l = T² ∙ g / 4 π ²
l = ( T² / 4 π ² ) ∙ g
l = ( T / 2 π )² ∙ g