2A:
b: \(\left(\dfrac{x}{2}-1\right)\left(\dfrac{x^2}{4}+\dfrac{x}{2}+1\right)=\dfrac{1}{8}x^3-1\)
c: \(\left(3x+y\right)\left(9x^2-3xy+y^2\right)=27x^3+y^3\)
d: \(\left(x^2-\dfrac{xy}{2}\right)\left(x^4+\dfrac{x^3y}{2}+\dfrac{x^2y^2}{4}\right)=x^6-\dfrac{1}{8}x^3y^3\)
Bài 16:
a: Ta có: \(N=100x^2-20x+1\)
\(=\left(10x-1\right)^2\)
\(=\left(10\cdot\dfrac{3}{10}-1\right)^2\)
=4
b: Ta có: \(P=25x^2-10xy^2+y^4\)
\(=\left(5x-y^2\right)^2\)
\(=\left(5\cdot5-4^2\right)^2\)
\(=9^2=81\)
Bài 14:
a: \(81^2=6561\)
b: \(102^2=10404\)
c: \(97\cdot103=100^2-9=9991\)
d: \(249\cdot351=300^2-51^2=87399\)
