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a,doi 20 phut =1/3 h
25 phut = 5/12 h
quang duong ab dai so km la 30. (1/3) + 5/12 . 12 = 15 (km)
b,vtb = 15/(1/3 +5/12) = 15/(3/4) = 20 (km/h)
vay................
1 ta co 55n+1 - 55n = 55n(55-1)=55n .54 vi 54 chia het cho 54 => 55n.54 chia het cho 54
=> 55^n+1 -55^n chia het cho 4
1, phan tich
a, x^2 +64
b, x^4 +x^2 +1
c, x^5 +x+1
d, x^7 +x^5 +1
2 a, (a+b)(a+b) = (a+b)^2
b,(a-b)(a+b) = a^2 - b^2
c,(a-b)(a-b) = (a-b)^2
ta co (a+2)^2 -(a+2)(a-2)
= a^2 +4a + 4 - a^2 +4
= 4a +8
= 4 (a+2)
chúc bạn học tốt
b, B= \(\dfrac{4^5.9^4-2.6^9}{2^{10}.3+6^8.20}\)
= \(\dfrac{\left(2^2\right)^5.\left(3^3\right)^4-2.6^9}{2^{10}.3+6^8.20}\)
=\(\dfrac{2^{10}.3^{12}-2.6^9}{2^{10}.3+6^8.20}\)
= \(\dfrac{3^{11}-6}{10}\)
a, ta có A.5 = 5 ( 1+5 +52 +...........+549 +550)
5A = 5 +52 +53 +............... + 550 +551
5A-A = (5 +52 +53 +............+ 551) - (1+5+52 +......+550)
4A = 551 -1
A =\(\dfrac{5^{51}-1}{4}\)
vậy A =
a, điều kiện để 5xny3 : 4x2y2
là x lớn hơn hoặc bằng 2
Not scotland again . It rained everyday last time , I want to go _______ sunny this summer
A someone B something C somebody D somewhere
she's very __ . she can be relied on to do her job properly
A efficient B cautious C serious d conservatie
there is a rumour that the army is about taking power ,tought this has been denied by government sources
A B C D