If it's not what You are looking for type in the equation solver your own equation and let us solve it.
D( n )
n = 0
n = 0
n = 0
n in (-oo:0) U (0:+oo)
42/21 = 6/n // - 6/n
42/21-(6/n) = 0
42/21-6*n^-1 = 0
-6*n^-1 = -2 // : -6
n^-1 = 1/3
-1 < 0
1/(n^1) = 1/3 // * n^1
1 = 1/3*n^1 // : 1/3
3 = n^1
n = 3
n = 3
| 3(7+x)=5(7-(-4)) | | 21/5-3 | | 49t^2-16= | | 2(x+1)=2x-3 | | 4c+5c-8c=13+6 | | 6y-14-3y=8(7-(-2)) | | -2n-(9n-9)= | | 3/5z+6/5 | | 1/4+7/8= | | (4x+5)(2x+3)=120 | | x+3+x-8+x=556 | | 3xy*3xy=0 | | 1225= | | (2x/5)-1=(x/3)+(1/15) | | 2(3y-1)-4=2y-(6-y) | | 2x+3xy+2y=10 | | 3(x+5)=7(2x+1) | | ax+bx+c=d | | 2x/5-1=x/3+1/15 | | 7x+30=-45-8x | | (4z+1)-(3z-5)=0 | | 5x+6-3x=4x+2 | | y/-2+(-4)=8 | | 8x+12=15+5x | | 6-5x=31 | | 165=5x^3 | | 48/r=12 | | 6x+(-3)=-12 | | 9h-3=1h | | 5x+41x+8=0 | | 4*21=7x | | -6y+4=5y-7 |