`a) (x-10).20=20`
`<=> x-10=20:20`
`<=> x-10=1`
`<=> x=10+1`
`<=> x=11`
`b) (3x-2^4).7^3=2.7^4`
`<=> (3x-16).7^3=2.7.7^3`
`<=> (3x-16).7^3=14.7^3`
`<=> 3x-16=14`
`<=> 3x=14+16`
`<=> 3x=30`
`<=> x=30:3`
`<=> x=10`
`c)` - Vì `x` chia `3` dư `2`, chia `4` dư `2`, chia `5` dư `2` nên ta có :
`x-2 vdots 3;4;5`
`=> x-2 in BC(3,4,5)`
- Vì `x<150`
`=> x-2<150-2`
`=> x-2<148`
- Ta có :
`3=3`
`4=2^2`
`5=5`
`=> BCN N(3,4,5)=2^2 .3.5=60`
`=> BC(3,4,5)=B(60)={0;60;120;180;...}`
vì `x-2 in BC(3,4,5)` và `x-2 <148`
`=> x-2 in {0;60;120}`
`=> x in {2;62;122}`