Here are the solutions to problems 1, 2, 3, and 4.
1. Find the binomial expansion of x2(x−2y)3.
Step 1: Expand (x−2y)3 using the binomial theorem (a+b)n=∑k=0n(kn)an−kbk.
Here, a=x, b=−2y, and n=3.
(x−2y)3=(03)x3(−2y)0+(13)x2(−2y)1+(23)x1(−2y)2+(33)x0(−2y)3
=1⋅x3⋅1+3⋅x2⋅(−2y)+3⋅x⋅(4y2)+1⋅1⋅(−8y3)
=x3−6x2y+12xy2−8y3
Step 2: Multiply the expanded expression by x2.
x2(x−2y)3=x2(x3−6x2y+12xy2−8y3)
=x2⋅x3−x2⋅6x2y+x2⋅12xy2−x2⋅8y3
=x5−6x4y+12x3y2−8x2y3
The binomial expansion is x5−6x4y+12x3y2−8x2y3.
2. Find the term independent of x in the expansion of (x−x3)4.
Step 1: Write the general term Tr+1 for the binomial expansion (a+b)n=∑r=0n(rn)an−rbr.
Here, a=x, b=−x3=−3x−1, and n=4.
Tr+1=(r4)(x)4−r(−3x−1)r
Tr+1=(r4)x4−r(−3)r(x−1)r
Tr+1=(r4)(−3)rx4−r−r
Tr+1=(r4)(−3)rx4−2r
Step 2: For the term independent of x, the power of x must be 0.
4−2r=0
2r=4
r=2
Step 3: Substitute r=2 back into the general term to find the term.
T2+1=T3=(24)(−3)2x4−2(2)
T3=2!(4−2)!4!(9)x0
T3=2×14×3×9×1