Áp dụng nhị thức Newton
a) $(2 x+1)^{4}= 16 x^{4}+32 x^{3}+24 x^{2}+8 x+1$
b) $(3 y-4)^{4}=81 y^{4}-432 y^{3}+864 y^{2}-768 y+256$
c) $\left(x+\frac{1}{2}\right)^{4}=x^{4}+2 x^{3}+\frac{3}{2} x^{2}+\frac{1}{2} x+\frac{1}{16}$
d) $\left(x-\frac{1}{3}\right)^{4}=x^{4}-\frac{4}{3} x^{3}+\frac{2}{3} x^{2}-\frac{4}{27} x+\frac{1}{81}$