Can anyone tell me the difference between the two lines below? I am getting different results but I expected them to produce similar results.

double lhs=y*log10(x);
double rhs=x*log10(y);

**

double lhs=log10(x);
double rhs=log10(y);
lhs*=y;
rhs*=x;

I am getting wrong answers for x=6,y=6 while submitting on codeforces but I am getting correct on VSCode.