Given that ${{\left( 1-2x \right)}^{n}}=1-ax+84{{x}^{2}}-...$, where $n0$, find the value of

Question

Given that ${{\left( 1-2x \right)}^{n}}=1-ax+84{{x}^{2}}-...$, where $n>0$, find the value of $n$ and of $a$.

Accepted Answer

$n=7,\ a=14$

Binomial Theorem