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To find the specified term in each binomial expansion, we use the binomial theorem. The general term T_r+1 in the expansion of (a+b)ⁿ is given by:

Mathematics

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3 parts
a

40x2y340x^2y^3

b

6x2y26x^2y^2

c

12xy212xy^2

Step-by-step solution

6 steps

To find the specified term in each binomial expansion, we use the binomial theorem. The general term Tr+1T_{r+1} in the expansion of (a+b)n(a+b)^n is given by:

Tr+1=(nr)an−rbrT_{r+1} = \binom{n}{r} a^{n-r} b^r

Part a· 2 steps

Find the term x2y3x^2y^3 in (2x+y)5(2x+y)^5.

  1. Identify aa, bb, and nn.

    In this expansion, a=2xa = 2x, b=yb = y, and n=5n = 5. We want the term with x2y3x^2y^3.
    Comparing brb^r with y3y^3, we get r=3r=3.
    Then n−r=5−3=2n-r = 5-3 = 2.
    The term is T3+1=(53)(2x)5−3(y)3T_{3+1} = \binom{5}{3} (2x)^{5-3} (y)^3.

  2. Calculate the binomial coefficient and simplify the term.

    T4=(53)(2x)2y3T_{4} = \binom{5}{3} (2x)^2 y^3 (53)=5!3!(5−3)!=5!3!2!=5×42×1=10\binom{5}{3} = \frac{5!}{3!(5-3)!} = \frac{5!}{3!2!} = \frac{5 \times 4}{2 \times 1} = 10 (2x)2=4x2(2x)^2 = 4x^2 T4=10⋅4x2⋅y3=40x2y3T_{4} = 10 \cdot 4x^2 \cdot y^3 = 40x^2y^3

    The term is 40x2y3\boxed{40x^2y^3}.

Part b

6x2y26x^2y^2

Find the term x2y2x^2y^2 in (x−y)4(x-y)^4.

  1. Identify aa, bb, and nn.

    In this expansion, a=xa = x, b=−yb = -y, and n=4n = 4. We want the term with x2y2x^2y^2.
    Comparing brb^r with (−y)r(-y)^r and the desired y2y^2, we get r=2r=2.
    Then n−r=4−2=2n-r = 4-2 = 2.
    The term is T2+1=(42)(x)4−2(−y)2T_{2+1} = \binom{4}{2} (x)^{4-2} (-y)^2.

  2. Calculate the binomial coefficient and simplify the term.

    T3=(42)x2(−y)2T_{3} = \binom{4}{2} x^2 (-y)^2 (42)=4!2!(4−2)!=4!2!2!=4×32×1=6\binom{4}{2} = \frac{4!}{2!(4-2)!} = \frac{4!}{2!2!} = \frac{4 \times 3}{2 \times 1} = 6 (−y)2=y2(-y)^2 = y^2 T3=6⋅x2⋅y2=6x2y2T_{3} = 6 \cdot x^2 \cdot y^2 = 6x^2y^2

    The term is 6x2y2\boxed{6x^2y^2}.

Part c

12xy212xy^2

Find the term xy2xy^2 in (x−2y)3(x-2y)^3.

  1. Identify aa, bb, and nn.

    In this expansion, a=xa = x, b=−2yb = -2y, and n=3n = 3. We want the term with xy2xy^2.
    Comparing brb^r with (−2y)r(-2y)^r and the desired y2y^2, we get r=2r=2.
    Then n−r=3−2=1n-r = 3-2 = 1.
    The term is T2+1=(32)(x)3−2(−2y)2T_{2+1} = \binom{3}{2} (x)^{3-2} (-2y)^2.

  2. Calculate the binomial coefficient and simplify the term.

    T3=(32)x1(−2y)2T_{3} = \binom{3}{2} x^1 (-2y)^2 (32)=3!2!(3−2)!=3!2!1!=31=3\binom{3}{2} = \frac{3!}{2!(3-2)!} = \frac{3!}{2!1!} = \frac{3}{1} = 3 (−2y)2=(−2)2y2=4y2(-2y)^2 = (-2)^2 y^2 = 4y^2 T3=3⋅x⋅4y2=12xy2T_{3} = 3 \cdot x \cdot 4y^2 = 12xy^2

    The term is 12xy2\boxed{12xy^2}.

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