1+1=2 nha ban

Vì \(\frac{a}{27}=\frac{-5}{9}\Rightarrow\frac{a}{27}=\frac{\left(-5\right).3}{9.3}\)

\(\Rightarrow\frac{a}{27}=\frac{-15}{27}\Rightarrow a=-15\)

Lại có: \(\frac{-5}{9}=\frac{-45}{b}\Rightarrow\frac{\left(-5\right).9}{9.9}=\frac{-45}{b}\)

\(\Rightarrow\frac{-45}{81}=\frac{-45}{b}\Rightarrow b=81\)

Vậy a=-15;b=81

4+5+6

=4+6+5

=10+5

=15

ai k mh mh k lại

kc ho mh nhadang quoc tuan

=15 nhé bạn

193 + 7 - 100

= 200 - 100

= 100

Đặt: nC2H5OH= x (mol), nCH3COOH= y (mol)

mhh= 46x + 60y= 10.6g (1)

C2H5OH + Na --> C2H5ONa + 1/2H2

CH3COOH + Na --> CH3COONa + 1/2H2

nH2= 0.5x + 0.5y= 0.1 (mol) (2)

Giải (1) và (2) :

x=y= 0.1

mC2H5OH= 4.6g

mCH3COOH= 6g

1+1=2 vì 1+1=2

Mặt trời, mặt trăng, sao

\(\frac{a}{27}=\frac{-5}{9}=\frac{-45}{b}\)

Vì \(\frac{a}{27}=\frac{-5}{9}\Rightarrow9.a=\left(-5\right).27=-135\Rightarrow a=\frac{-135}{9}=-15\)

Vì \(\frac{-5}{9}=\frac{-45}{b}\Rightarrow-5.b=\left(-45\right).9=-405\Rightarrow b=\frac{-405}{-5}=\frac{405}{5}=81\)

Vậy a=-15;b=81

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+.....+\frac{1}{42}\)

=\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+..........+\frac{1}{6.7}\)

=\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+.........+\frac{1}{6}-\frac{1}{7}\)

=\(1-\frac{1}{7}\)

=\(\frac{6}{7}\)