$\displaystyle
t=2(pi)\sqrt\frac{100-L}{g}
$
i have to make L subject. and find L when t=20 g =2
i have $\displaystyle g(\frac{t}{2pi})^2-100 = L$
not sure on this one? do i remove the sqrt first or bring the 2pi across first?
thanks
$\displaystyle T = 2\pi \sqrt{\frac{100-L}{g}}
$
$\displaystyle \frac{T}{2\pi} = \sqrt{\frac{100-L}{g}}$
$\displaystyle \left(\frac{T}{2\pi}\right)^2 = \frac{100-L}{g}$
$\displaystyle g \cdot \left(\frac{T}{2\pi}\right)^2 = 100-L$
$\displaystyle L = 100 - g \cdot \left(\frac{T}{2\pi}\right)^2$