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WAEC Further Mathematics 2016 Paper

Question : 16

Total: 40

Find the fourth term in the expansion of

(3x - y)^{6}

$-540x^{3}y^{3}$
$-540x^{4}y^{2}$
$-27x^{3}y^{3}$
$540x^{4}y^{2}$

Validate

Solution:

Listing out in order, the terms of this expansion have coefficients: ${}^{6}C_{6}, {}^{6}C_{5}, {}^{6}C_{4}, {}^{6}C_{3}, {}^{6}C_{2}, {}^{6}C_{1}, {}^{6}C_{0}$

The 4th term = ${}^{6}C_{3}(3x)^{3}(-y)^{3} = 20 \times 27x^{3} \times -y^{3}$

= $-540x^{3}y^{3}$ .

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