Question

Find forth term in the expansion of (x-2y)¹²

• A. $$-1760x^9y^3$$
• B. $$-176x^9y^3$$
• C. $$60x^9y^3$$
• D. $$1760x^9y^3$$

Answer 1

Answer:

$$-1760x^9y^3$$

$T_{r+1}=^nC_ra^{n-r}b^r$

$T_4=^{12}C_3x^9(-2y)^3$

$=\frac{12!}{3! \times 9!}x^9-8 \times y^3$

$=\frac{12 \times 11 \times 9!}{3! \times 9!}-8x^9y^3$

$=2 \times 11 \times 10 \times -8 x^9 y^3$

$=-1760x^9y^3$