Question 155827
A general expansion would be,
{{{(a + b)^5 = a^5+5a^4b + 10a^3b^2 +10a^2b^3 +5ab^4 + b^5}}}
Let {{{a=y^-3}}} and {{{b=y^2}}}, the term not involving y will have y canceling out in the numerator and denominator.
{{{a^2=y^-6}}}
{{{b^3=y^6}}}
{{{a^2b^3=y^-6*y^6=y^(-6+6)=1}}}
That's the third term of the expansion, {{{10a^2b^3=10(1)=10}}}.