Chi minh lam bai nay voi, xin may ban do

11/9-3/9.4/5=8/9.4/5=32/45

học tốt

11/9-3/9 x 4/5=11/9-4/15

                      =55/45-12/45

                      =43/45

\(\frac{11}{9}\)- \(\frac{3}{9}x\frac{4}{5}\)= \(\frac{8}{9}\)x \(\frac{4}{5}\)= \(\frac{32}{45}\)

\(a,\dfrac{5}{9}\times\dfrac{5}{2}+\dfrac{4}{9}\times\dfrac{5}{2}=\dfrac{5}{2}\times\left(\dfrac{5}{9}+\dfrac{4}{9}\right)=\dfrac{5}{2}\times1=\dfrac{5}{2}\)

\(12\times\dfrac{3}{4}-\dfrac{3}{4}\times\dfrac{12}{7}=\dfrac{3}{4}\times\left(12-\dfrac{12}{7}\right)=\dfrac{3}{4}\times\dfrac{72}{7}=\dfrac{54}{7}\)

1+2+3+4+5+6+7+8+9

=(1+9)+(2+8)+(3+7)+(4+6)+5

=10+10+10+10+5

=40+5

=45

= (1 + 9 ) + ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + 5

=10 + 10 + 10 + 10 + 5

= 40 + 5 

= 45

Ta có:

9⁷ + 81⁴ - 27⁵

= (3²)⁷ + (3⁴)⁴ - (3³)⁵

= 3¹⁴ + 3¹⁶ - 3¹⁵

= 3¹⁴.(1 + 3² - 3)

= 3¹⁴.(1 + 9 - 3)

= 3¹⁴.7 chia hết cho 7 (đpcm)