100=60/(1/4*3.14*d^2)

Solution for 100=60/(1/4*3.14*d^2) equation:

D( d )

3.14*(1/4)*d^2 = 0

3.14*(1/4)*d^2 = 0

3.14*(1/4)*d^2 = 0

0.785*d^2 = 0 // : 0.785

d^2 = 0

d = 0

d in (-oo:0) U (0:+oo)

100 = 60/(3.14*(1/4)*d^2) // - 60/(3.14*(1/4)*d^2)

100-(60/(3.14*(1/4)*d^2)) = 0

100-76.43312102*d^-2 = 0

-76.43312102*d^-2 = -100 // : -76.43312102

d^-2 = 1.30833333

-2 < 0

1/(d^2) = 1.30833333 // * d^2

1 = 1.30833333*d^2 // : 1.30833333

0.76433121 = d^2

d^2 = 0.76433121 // ^ 1/2

abs(d) = 0.76433121^(1/2)

d = 0.76433121^(1/2) or d = -0.76433121^(1/2)

d in { 0.76433121^(1/2), -0.76433121^(1/2) }