cho x-y =7 . cm cac bieu thuc sau chia het cho 7:
a, 22x – y
b, 8x + 20y
c, 11x + 10y
cho x-y =7 . cm cac bieu thuc sau chia het cho 7: a, 22x – y b, 8x + 20y c, 11x + 10y
By Ruby
By Ruby
cho x-y =7 . cm cac bieu thuc sau chia het cho 7:
a, 22x – y
b, 8x + 20y
c, 11x + 10y
`a, 22x – y`
`= 21x + x – y`
`= 21x + (x-y)`
Vì `21x \vdots 7` và `x-y \vdots 7`
`⇒ 22x – y \vdots 7`
`b, 8x + 20y`
`= 14x – 6x + 14y + 6y`
`= (14x + 14y) – (6x – 6y)`
`= 14(x+y) – 6(x-y)`
Vì `14(x+y) \vdots 7` và `6(x-y) = 6.7 \vdots 7`
`=> 8x + 20y \vdots 7`
`c, 11x + 10y`
`= 14x – 3x + 7y + 3y`
`= (14 x + 7y) – (3x – 3y)`
`= 7(2x+y) – 3(x-y)`
Vì `7(2x+y)\vdots7` và `3(x-y)=3.7\vdots7`
`=> 11x + 10y\vdots7`
Đáp án:
Giải thích các bước giải:
Vì `x-y=7`
`->x=7+y`
a,
`22x-y`
`=22(7+y)-y`
`=154+22y-y`
`=154+21y`
`=7.(22+3y)`
Do `7 \vdots 7`
`=>7.(22+3y) \vdots 7`
`=>(22x-y) \vdots 7`
b,
`8x+20y`
`=8.(7+y)+20y`
`=56+8y+20y`
`=56+28y`
`=7.(8+4y)`
Do `7 \vdots 7`
`=>7.(8+4y) \vdots 7`
`=>8x+20y \vdots 7`
c,
`11x+10y`
`=11.(7+y)+10y`
`=77+11y+10y`
`=77+21y`
`=7.(11+3y)`
Do `7 \vdots 7`
`=>7.(11+3y) \vdots 7`
`=>11x+10y \vdots 7`