F.3 Maths

1) a=b+3cd/b-3cd
a(b-3cd)=b+3cd
ab-3acd=b+3cd
ab-b=3cd+3acd
b(a-1)=3cd(1+a)
c=b(a-1)/3cd(1+a) //

2) s=n/2[2a+(n-1)d]
s=n/4a+2nd-2d
s(4a+2nd-2d)=n
4as+2nds-2ds=n
2nds-2ds=n-4as
2ds(n-1)=n-4as
d=n-4as/2s(n-1) //

1)c=b/3d
2)d=(sn-4a)/(2n-2)