Cách làm cho bạn:
Ta có:
a) $\frac{1}{4}.x(\frac{1}{2}x^{2}).(\frac{−4}{5}x^{3})$
$=\frac{−1}{10}x^{6}$
b) $0,5x^{m+1}.0,8x^{m−1}$
$=0,4x^{2m}$
c) $(x^{2}−3x+\frac{1}{4})(−3x^{3})$
$=−3x^{5}+9x^{4}−\frac{3}{4}x^{3}$;
d) $(x−2)(x^{2}+x−1)−x(x^{2}−1)$
$= −x^{2}−2x+2$
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