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Gọi hai số tự nhiên thỏa mãn đề bài theo thứ tự từ bé đến lớn lần lượt là:
b ; a 300 ≤ b < a ≤ 400;
Ta có: a - b = 84 và ƯCLN(a,b) = 84
⇒ \(\left\{{}\begin{matrix}a=28\times c\\b=28\times d\end{matrix}\right.\) (c; d) = 1
28 \(\times\) c - 28 \(\times\) d = 84
28\(\times\)(c-d) = 84
c - d = 3 ⇒ d = c - 3
Mặt khác ta cũng có: 300 ≤ a ≤ 400 ⇒ 300 ≤ 28 \(\times\) c ≤ 400
⇒\(\dfrac{75}{7}\) ≤ c ≤ \(\dfrac{100}{7}\) ⇒ 10,7 ≤ c ≤ 14,2 vì c \(\in\) N nên c = 11; 12; 13
lập bảng ta có:
| c | 11 | 12 | 13 |
| d = c - 3 | 8 | 9 (loại) | 10 |
| a = 28 \(\times\) c | 308 | 364 | |
| b = 28 \(\times\) d | 224 | 280 |
Theo bảng trên ta có hai cặp số tự nhiên thỏa mãn đề bài là:
(224; 308) và (280; 364)
Ta có:
\(8=2^3\)
\(18=2.3^2\)
\(28=2^2.7\)
\(\Rightarrow BCNN\left(8,18,28\right)=2^3.3^2.7=504\)
Phân tích ra thừa số nguyên tố:
8 = 23
18 = 2 . 32
28 = 22 . 7
⇒ BCNN(8,18,28)= 23. 32. 7 = 504
Vì 14 chia hết cho 2x Nên => 7 chia hết cho x
Mà 7 chia hết cho x nên => x \(\in\) Ư ( 7 ) = { 1 , 7 }
Vậy: Số tự nhiên 14 chia hết cho 2x là : 1 và 7
\(14⋮2x\Rightarrow2x\inƯ\left(14\right)\\ Ư\left(14\right)=\left\{-1;1;2;-2;4;-4;7;-7;-14;14\right\}\)
\(Th1:2x=-1\\ x=-\dfrac{1}{2}\\ Th2:2x=1\\ x=\dfrac{1}{2}\\ Th3:2x=2\\ x=1\\ Th4:2x=-2\\ x=-1\\ Th5:2x=4\\ x=2\\ Th6:2x=-4\\ x=-2\\ Th7:2x=-7\\ x=-\dfrac{7}{2}\\ Th8:2x=7\\ x=\dfrac{7}{2}\\ Th9:2x=14\\ x=7\\ Th10:2x=-14\\ x=-7\)
Vậy x ϵ....
`@` `\text {Ans}`
`1/2+1/8+1/12`
`=`\(\dfrac{12}{24}+\dfrac{3}{24}+\dfrac{2}{24}\)
`=`\(\dfrac{17}{24}\)
`@` `\text {Ans}`
`a,`
`-2/3+2x=4/3`
`=> 2x=4/3 - (-2/3)`
`=> 2x=4/3+2/3`
`=> 2x=2`
`=> x=1`
`b,`
`5/8 - 5 \div x = -3/8`
`=> 5 \div x=5/8 - (-3/8)`
`=> 5 \div x= 5/8+3/8`
`=> 5 \div x=1`
`=> x = 5\div 1`
`=> x=5`
`c,`
`2/3 - x = -1/2`
`=> x= 2/3 - (-1/2)`
`=> x=2/3+1/2`
`=> x=7/6`
`d,`
`5/7 - 4x=-51/7`
`=> 4x= 5/7 - (-51/7)`
`=> 4x=5/7+51/7`
`=> 4x=8`
`=> x= 8 \div 4`
`=> x=2`
`e,`
`-7/x+8/15 = -1/20`
`=> -7/x = -1/20 - 8/15`
`=> -7/x=-7/12`
`=> x=12`
`f,`
`5/3 - (x-1 1/5) = (-5/4 - 1 1/2) - 7/8`
`=> 5/3 - (x- 1 1/5) = -11/4-7/8`
`=> x-1 1/5= 5/3 - (-11/4 - 7/8)`
`=> x- 1 1/5= 5/3 - (-29/8)`
`=> x- 1 1/5=127/24`
`=> x=127/24 + 1 1/5`
`=> x=779/120`
On my first day at school, I was very excited as I was not going to be a primary schooler but a secondary schooler. I was very happy as it was very easy to make friends and the teacher's were very nice and friendly. Friend's were playful and jolly. Not only that but the food there was awesome. The food was filled with wonderful flavours. The classroom decorations was nice and it was very clean. The entrance was also welcoming. I hope that I will make lot's of friends in school too!
Tham khảo nhá :)
Hai số nguyên tố cùng nhau: x và y là hai số nguyên tố cùng nhau có ƯCLN(a,b)=1
VD: 5 và 2 là hai số nguyên tố cùng nhau vì ƯCLN(5,2)=1
\(\left(1+\dfrac{1}{2}\right)\times\left(1+\dfrac{1}{3}\right)\times\left(1+\dfrac{1}{4}\right)\times....\times\left(1+\dfrac{1}{98}\right)\times\left(1+\dfrac{1}{99}\right)\)
\(=\dfrac{3}{2}\times\dfrac{4}{3}\times\dfrac{5}{4}\times...\times\dfrac{99}{98}\times\dfrac{100}{99}\)
\(=\dfrac{1\times100}{2\times1}\)
\(=\dfrac{100}{2}\\ =50\)
1.lived
2.Did you go to
3.doesn't like,isn't
4.listen,don't listen
5.play,am not(ko chắc nữa..)
1. I lived in Hanoi 10 years ago.
2. Did you go sailing when you were a child?
3. My father didn't like vegetables, but he doesn't now.
4. They listen to rock music, but they don't listen any more.
5. I played tennis, but now I don't. (có thể là thế)