1/15

giup minh voi, di ma

\(\dfrac{1}{2}\times\left(\dfrac{1}{3}-\dfrac{1}{5}\right)=\dfrac{1}{2}\times\left(\dfrac{5}{15}-\dfrac{3}{15}\right)=\dfrac{1}{2}\times\dfrac{2}{15}=\dfrac{1}{15}\)

4/15

4/15

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

=1/4+7/8=9/8

\(\dfrac{1}{4}+\dfrac{3}{4}:\dfrac{-6}{-7}=\dfrac{1}{4}+\dfrac{3}{4}:\dfrac{6}{7}=\dfrac{1}{4}+\dfrac{3}{4}\times\dfrac{7}{6}=\dfrac{1}{4}+\dfrac{7}{8}=\dfrac{9}{8}\)

ko rảnh giải chi tiết nên:

\(\dfrac{9}{8}\)

\(\dfrac{7}{5}\times\dfrac{4}{3}\times\dfrac{4}{3}\)

\(=\dfrac{28}{15}\times\dfrac{4}{3}\)

\(=\dfrac{112}{45}\)

\(\dfrac{7}{5}\times\dfrac{4}{3}\times\dfrac{4}{3}=\dfrac{28}{15}\times\dfrac{4}{3}=\dfrac{28\times4}{15\times3}=\dfrac{112}{45}\)

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

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

x-28=-15

x=13

      Vậy x=13

thank you, trinh thanh cong

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

      = (x^4-x^2) + (4x^2-4x)

      = x^2(x^2-1) + 4(x^2-1)

      = (x^2+4)(x^2-1)

Do đó ta có: h(x)=0 hay (x^2+4)(x^2-1)=0

                           Suy ra           x^2-1=0 (vì x^2+4 >0)

                                                x^2   =1

                                             =>x=1 hay x= -1.