If it's not what You are looking for type in the equation solver your own equation and let us solve it.
D( d )
3*d^2+100 = 0
3*d^2+100 = 0
3*d^2+100 = 0
3*d^2 = -100 // : 3
d^2 = -100/3
d in (-oo:+oo)
5.7 = (1000+3900)/(3*d^2+100) // - (1000+3900)/(3*d^2+100)
5.7-((1000+3900)/(3*d^2+100)) = 0
(-1*4900)/(3*d^2+100)+5.7 = 0
(-1*4900)/(3*d^2+100)+(5.7*(3*d^2+100))/(3*d^2+100) = 0
5.7*(3*d^2+100)-1*4900 = 0
17.1*d^2-4330 = 0
(17.1*d^2-4330)/(3*d^2+100) = 0
(17.1*d^2-4330)/(3*d^2+100) = 0 // * 3*d^2+100
17.1*d^2-4330 = 0
17.1*d^2 = 4330 // : 17.1
d^2 = 253.21637427
d^2 = 253.21637427 // ^ 1/2
abs(d) = 253.21637427^(1/2)
d = 253.21637427^(1/2) or d = -253.21637427^(1/2)
d in { 253.21637427^(1/2), -253.21637427^(1/2) }
| x9y6/x3y2 | | 5,6=1,176 | | 1.7=.4x-78.46 | | 600=101x-201513 | | 3-4t-4t^2=0 | | 5x^2-25x+13=y | | 7+6x=52 | | 3x-8+4-2x=4 | | 15x-12+16x-14=37 | | 9x-23=4x | | 3x^2-3x-270=0 | | 2m-12+38=-18 | | (1.05)x=2.5 | | 9w^3+12v^2w/9w^3x^3 | | 6y+4y=60 | | .5t+.6=.4-t | | -2b-13=4d-10 | | (2x+5)(x-2x+1)= | | -16.8=-5.6c | | -0.8x+0.4x+8=2 | | 2a(2a+5)= | | 89-4x=14x+15 | | 5(3+2k)+3(2+3k)= | | 9.5x+10.08=-10.5x+9.12 | | 120+4x=8x+10 | | 7.5x-2.8=27.2 | | (3/x+6)+(7/x-2) | | 0=W^2+9 | | -6(t-2)-(t+6)=6 | | 125=5s+10c | | (5n+5/5n^2+35n-40)+(7n/3n) | | 1-x/x+2=7/x |