Answer:
-66 x^9 y^3
Explanation:
(r + 1)th term of (a + b)^n = nCr a^(n-r) b^r
so the 4th term of (x - y)^12
= 12C2 x^(12-3) (-y)^3
= 66 x^9 (-y)^3
= -66 x^9 y^3 (answer)
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