Giúp e với ạ e cần gấp

`5.`

`a)`

        `11/19 +19/18 + 8/19 -1/18+5,2`

`=(11/19+ 8/19)+(19/18- 1/18)+5,2`

`=1+1+5,2`

`=7,2`

`b)`

       `3/7 . 16/15 - 3/7. 2/15`

`=3/7 .(16/15- 2/15)`

`=6/14 . 14/15`

`=6/15=2/5`

`c)`

       `(5/12 :3 2/6)+(2/3-1/2)^2`

`=(5/12 : 10/3) + (4/6-3/6)^2`

`= (5/12 .3/10)+ (1/6)^2`

`=1/8 +1/36`

`=9/72 + 2/72`

`=11/72`

`6.`

`a)`

       `x+3/8=1/5`

`⇒x=1/5-3/8`

`⇒x=8/40-15/40`

`⇒x=-7/40`

Vậy, `x=-7/40`

`b)`

       `1/2+2/3x=4/5`

`⇒2/3x=4/5-1/2`

`⇒2/3x=8/10-5/10`

`⇒2/3x=3/10`

`⇒x=3/10: 2/3`

`⇒x=3/10. 3/2`

`⇒x=9/20`

Vậy, `x=9/20`

`7.`

Ta có: `2^90=(2^10)^9=1024^9`

           `5^36=(5^4)^9 = 625^9`

Vì `1024^9 > 625^9`

`⇒2^90: 5^36`

Vậy, `2^90: 5^36`

`#` $kiddd$