4/15

4/15

\(\dfrac{8}{30}=\dfrac{4\times2}{15\times2}=\dfrac{4}{15}\)

a.\(=\dfrac{8}{15}\times\dfrac{1}{2}=\dfrac{4}{15}\)

b.\(=\dfrac{1}{3}\times\dfrac{1}{2}-\dfrac{1}{5}\times\dfrac{1}{2}=\dfrac{1}{6}-\dfrac{1}{10}=\dfrac{1}{15}\)

a.(1/3+1/5) x 1/2

=8/15 x 1/2=8/30=4/15

b)(1/3-1/5) x 1/2=2/15 x 1/2=1/15

-x-20-(8-2x)=(-12-3)

-x-20-8+2x=-15

x-28=-15

x=13

      Vậy x=13

thank you, trinh thanh cong

\(x+3\frac{1}{2}=24\frac{1}{4}-x\)

\(\Leftrightarrow x+x=24\frac{1}{4}-3\frac{1}{2}\)

\(\Leftrightarrow2x=\frac{94}{4}-\frac{14}{4}\)

\(\Leftrightarrow2x=\frac{90}{4}=\frac{45}{2}\)

\(\Leftrightarrow x=\frac{45}{2}:2\)

\(\Leftrightarrow x=\frac{45}{4}\)

mình trả lời đầu tiên nè

\(PT\Leftrightarrow5-6+x=12-8x\)

\(\Leftrightarrow9x=13\)

\(\Leftrightarrow x=\dfrac{13}{9}\)

Vậy: \(S=\left\{\dfrac{13}{9}\right\}\)

\(5-\left(6-x\right)=4\left(3-2x\right)\)

\(5-6+x=12-8x\)

\(-1+x=12-8x\)

\(x-1=12-8x\)

\(12+1=8x+1\)

\(8x=13-1\)

\(x=12:8\)

\(x=\dfrac{12}{8}=\dfrac{3}{2}\)

\(\frac{1}{\sqrt{a}+\sqrt{a+1}}=\frac{\sqrt{a+1}-\sqrt{a}}{\left(\sqrt{a}+\sqrt{a+1}\right)\left(\sqrt{a+1}-\sqrt{a}\right)}=\frac{\sqrt{a+1}-\sqrt{a}}{a+1-a}=\sqrt{a+1}-\sqrt{a}\Rightarrow\frac{1}{1+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+.......+\frac{1}{\sqrt{99}+\sqrt{100}}=-1+\sqrt{2}-\sqrt{2}+\sqrt{3}-......-\sqrt{99}+\sqrt{100}=10-1=9\)