ko bt ccc

4^3=64               5^2=10

64 x 125 - 125 x 10 

= 8000 - 1250 

=6750 

đáp án : 6750

a: \(6^x=5\)

=>\(x=log_65\)

b: \(7^{3-x}=5\)

=>\(3-x=log_75\)

=>\(x=3-log_75\)

c: \(\left(\dfrac{3}{5}\right)^{x-2}=\dfrac{27}{125}\)

=>\(\left(\dfrac{3}{5}\right)^{x-2}=\left(\dfrac{3}{5}\right)^3\)

=>x-2=3

=>x=5

d: \(\left(\dfrac{4}{5}\right)^x=\dfrac{5}{4}\)

=>\(\left(\dfrac{4}{5}\right)^x=\left(\dfrac{4}{5}\right)^{-1}\)

=>x=-1

a.

\(6^x=5\Rightarrow x=log_65\)

b.

\(7^{3-x}=5\Rightarrow3-x=log_75\)

\(\Rightarrow x=3-log_75\)

c.

\(\left(\dfrac{3}{5}\right)^{x-2}=\dfrac{27}{125}\Rightarrow x-2=log_{\dfrac{3}{5}}\left(\dfrac{27}{125}\right)\)

\(\Rightarrow x-2=3\Rightarrow x=5\)

d.

\(\left(\dfrac{4}{5}\right)^x=\dfrac{5}{4}\Rightarrow\left(\dfrac{4}{5}\right)^x=\left(\dfrac{4}{5}\right)^{-1}\)

\(\Rightarrow x=-1\)

c: (x-y+4)^2

=x^2+y^2+16+2*x*(-y)-2*y*4+2*x*4

=x^2+y^2+16-2xy-8y+8x

h; x^3y^6z^9-125

\(=\left(xy^2z^3\right)^3-5^3\)

\(=\left(xy^2z^3-5\right)\left(x^2y^4z^6+5xy^2z^3+25\right)\)

b: Ta có: \(\left(x+5\right)^3-x^3-125\)

\(=x^3+15x^2+75x+125-x^3-125\)

\(=15x^2+75x\)

\(25\times20\times125\times8-8\times30\times5\times125\\ =125\times500\times8-8\times150\times125\\ =125\times4000-1200\times125\\ =125\times\left(4000-1200\right)\\ =125\times2800\\ =350000\)