X=1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17

( x + 2 . 9 ) : 4 .2 =56

( x + 2 . 9 ) : 4 =56 : 2 

( x + 2 . 9 ) : 4 = 28

( x + 2 . 9 ) =  28 . 4 

( x + 2 . 9 ) = 112

x+ 18 =112

x = 112 - 18 

x = 94

Vậy x = 94

****

 gợi ý nè 

Q(7) = 2016 

270*20+58*270+28*270=270*/20+58+28\=270*100=270 

\(\Leftrightarrow x-\dfrac{3^{17}-3^{18}}{3^{16}\cdot5+3^{16}\cdot7}=0\)

=>\(x=\dfrac{3^{17}\left(1-3\right)}{3^{16}\left(5+7\right)}=3\cdot\dfrac{-2}{12}=-3\cdot\dfrac{1}{6}=-\dfrac{1}{2}\)

\(a,6,7\%+5,96\%=0,067+0,0596=0,1266\)

\(b,96,8\%-54,9\%+4,5\%=0,986-0,549+0,045=0,482\)

\(c,9\times8,7\%=9\times0,087=0,783\)

\(d,96,5\%:5=0,965:5=0,193\)

A. 12.66 %

B. 46.4 %

C. 78.3 %

D . 19.3 %

ĐKXĐ:\(x\ne0,x\ne-12\)

\(\dfrac{270}{x}-\dfrac{270}{x+12}=\dfrac{7}{10}\\ \Leftrightarrow270\left(\dfrac{1}{x}-\dfrac{1}{x+12}\right)=\dfrac{7}{10}\\ \Leftrightarrow\dfrac{x+12-x}{x\left(x+12\right)}=\dfrac{7}{2700}\\ \Leftrightarrow\dfrac{12}{x^2+12x}=\dfrac{7}{2700}\\ \Leftrightarrow7x^2+84x-32400=0\)

Xem lại đề

ko bt lm

ĐKXĐ: x∉{0;-2}

Ta có; \(\frac{270}{x+2}+\frac{7}{10}=\frac{270}{x}\)

=>\(\frac{270}{x}-\frac{270}{x+2}=\frac{7}{10}\)

=>\(\frac{270\left(x+2\right)-270x}{x\left(x+2\right)}=\frac{7}{10}\)

=>\(\frac{270x+540-270x}{x\left(x+2\right)}=\frac{7}{10}\)

=>7x(x+2)=5400

=>\(7x^2+14x-5400=0\)

=>\(x^2+2x-\frac{5400}{7}=0\)

=>\(x^2+2x+1-\frac{5407}{7}=0\)

=>\(\left(x+1\right)^2=\frac{5407}{7}\)

=>\(x+1=\pm\sqrt{\frac{5407}{7}}\)

=>\(x=-1\pm\sqrt{\frac{5407}{7}}\) (nhận)