Bài 24
a ) Với x = 4 ta có :
`A = ( 8/5 - 1/2 × 4/5 ) : 1/5`
`A = ( 8/5 - 2/5 ) : 1/5`
`A = 6/5 : 1/5`
`A = 30/5 = 6`
Với x = 5 ta có :
`A = ( 8/5 - 1/2 × 5/5 ) : 1/5`
`A = ( 8/5 - 1/2 ) : 1/5`
`A = 11/10 : 1/5`
`A = 55/10`
Với x = 7 ta có :
`A = ( 8/5 - 1/2 × 7/5 ) : 1/5`
`A = ( 8/5 - 7/10 ) : 1/5`
`A = 9/10 : 1/5`
`A = 45/10`
b ) Với A = 4 ta có :
`( 8/5 - 1/2 × x/5 ) : 1/5 = 4`
`( 8/5 - 1/2 × x/5 ) = 4 × 1/5`
`( 8/5 - 1/2 × x/5 ) = 4/5`
`1/2 × x/5 = 8/5 - 4/5`
`1/2 × x/5 = 4/5`
`x/5 = 4/5 : 1/2`
`x/5 = 8/5`
`=> x = 8`
Với A = 6 ta có :
`( 8/5 - 1/2 × x/5 ) : 1/5 = 6`
`( 8/5 - 1/2 × x/5 ) = 6 × 1/5`
`( 8/5 - 1/2 × x/5 ) = 6/5`
`1/2 × x/5 = 8/5 - 6/5`
`1/2 × x/5 = 2/5`
`x/5 = 2/5 : 1/2`
`x/5 = 4/5`
`=> x = 4`
Với A = 11 ta có :
`( 8/5 - 1/2 × x/5 ) : 1/5 = 11`
`( 8/5 - 1/2 × x/5 ) = 11 × 1/5`
`( 8/5 - 1/2 × x/5 ) = 11/5`
`1/2 × x/5 = 11/5 - 8/5`
`1/2 × x/5 = 3/5`
`x/5 = 3/5 : 1/2`
`x/5 = 6/5`
`=> x = 6`
Với A = 25 ta có :
`( 8/5 - 1/2 × x/5 ) : 1/5 = 25`
`( 8/5 - 1/2 × x/5 ) = 25 × 1/5`
`( 8/5 - 1/2 × x/5 ) = 5`
`1/2 × x/5 = 5 - 8/5`
`1/2 × x/5 = 17/5`
`x/5 = 17/5 : 1/2`
`x/5 = 34/5`
`=> x = 34`
`#dtkc`
