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các bạn cho mình vài li-ke cho đủ 485 với 

cần làm nữa ko

Câu 10: Tìm x, biết

a)\(\left(-1\dfrac{2}{5}+x\right)\div\dfrac{14}{15}=2\dfrac{1}{3}\)

\(\Leftrightarrow-1\dfrac{2}{5}+x=\dfrac{98}{45}\)

\(\Leftrightarrow x=\dfrac{161}{45}\)

Câu b) đề sai phải ko bạn

\(x^3-x^2y-x+y\)

\(=\left(x^3-x^2y\right)-\left(x-y\right)\)

\(=x^2\left(x-y\right)-\left(x-y\right)\)

\(=\left(x-y\right)\left(x^2-1\right)\)

\(=\left(x-y\right)\left(x-1\right)\left(x+1\right)\)

\(3x-7x+2\)

\(=x\left(3-7\right)+2\)

\(=-4x+2\)

\(=2\left(-2x+1\right)\)

\(x^4+4\)

\(=x^4+4x^2+4-4x^2\)

\(=\left[\left(x^2\right)^2+2.x^2.2+2^2\right]-4x^2\)

\(=\left(x^2+2\right)^2-\left(2x\right)^2\)

\(=\left(x^2+2-2x\right)\left(x^2+2+2x\right)\)

b)\(x^2-7x+xy-7y\)

\(=x^2+xy-7x-7y\)

\(=\left(x^2+xy\right)-\left(7x+7y\right)\)

\(=x\left(x+y\right)-7\left(x+y\right)\)

\(=\left(x+y\right)\left(x-7\right)\)

Tính:

b)\(\dfrac{8^{20}+4^{20}}{4^{25}+64^5}\)

\(=\dfrac{\left(2^3\right)^{20}+\left(2^2\right)^{20}}{\left(2^2\right)^{25}+\left(2^6\right)^5}\)

\(=\dfrac{2^{60}+2^{20}}{2^{50}+2^{30}}\)

\(=\dfrac{2^{40}\left(2^{20}+1\right)}{2^{30}\left(2^{20}+1\right)}\)

\(=\dfrac{2^{40}}{2^{30}}\)

\(=2^{40-30}\)

\(=2^{10}\)

\(=1024\)

Tính:

a)\(\dfrac{8^{20}.4^{10}}{16^{21}}\)

\(=\dfrac{\left(2^3\right)^{20}.\left(2^2\right)^{10}}{\left(2^4\right)^{21}}\)

\(=\dfrac{2^{60}.2^{20}}{2^{84}}\)

\(=\dfrac{2^{80}}{2^{84}}\)

\(=2^{80-84}\)

\(=2^{-4}\)

\(=\dfrac{1}{16}\)