We know that the (r + 1)th term in the expansion of $(x + a)^n$ is given by $T_{r+1}$ = $\,{}^{n}C_r x^{n-r} a^r$ Then (r + 1)th term in the expansion of $(x+(-2y))^{12}$ is given by $T_{r+1}$ = $\,{}^{12}C_r x^{12-r} (-2y)^r$ For 4th term, we have r + 1 = 4 ⇒ r = 3 Substituting r = 3 in (i), we get $T_4$ = $\,{}^{12}C_3 x^{12-3} (-2y)^3$ = $220x^9(-8)y^3$ = - 1760 $x^9y^3$