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nè bạn thích trang trí bằng hoa gi hoa tuoi đi vì nó thom va dep don gian vay thoi k tui nha
S=5+5^2+5^3+5^4+...5^99
=> 5S=5^2+5^3+5^4+...5^100
=> 5S-S=4S=(5^2+5^3+5^4+...5^100)-(5+5^2+5^3+5^4+...5^99)
=> 4S = 5100-5
=> S=(5100-5)/4
S=5*5^2*5^3*5^4*...5^99
=> S=51+2+3+...+99
=> S=5((99+1).99):2
=> S=54950
(3x-2)+16=125+12
(3x-2)+16=137
3x-2=121
3x=123
x=41
5s=5^2+5^3+5^4+5^5+......+5^100
5s-s=5^100-5
4s=5^100-5
s=(5^100-5):4
kick nhé
\(\left(3x-2\right)^2+4^2=5^3+3.2^2\\ \Rightarrow\left(3x-2\right)^2+16=125+12\\ \Rightarrow\left(3x-2\right)^2=121\\ \Rightarrow3x-2=11\\ \Rightarrow x=\frac{13}{3}\)
S= \(5+5^2+5^3+.....+5^{99}\\ \Rightarrow5S=5^2+5^3+5^4+.....+5^{100}\\ \Rightarrow4S=5^{100}-5\\ \Rightarrow\frac{5^{100}-5}{4}\)
S=\(5.5^2.5^3.5^4.........5^{99}=5^{1+2+3+4+....+99}=5^{4950}\)
S=5+52+53+54+...+599
5S=52+53+54+...+599
5S-S=(52-52)+(53-53)+...+(599-599)+5100+5
S=(5100+5):4
k(k+1)(k+2)(k+3)-(k-1)k(k+1)(k+2)=k(k+1)(k+2).[(k+3)-(k-1)]=4k(k+1)(k+2)
=>đpcm
k(k+1)(k+2)(k+3)-(k-1)k(k+1)(k+2)
=k(k+1)(k+2).[(k+3)-(k-1)
=4k(k+1)(k+2)
=>Dqcm
k(k+1)(k+2)-(k-1)k(k+1)=k(k+1)(k+2-k+1)=3.k.(k+1)
S=1.2+2.3+3.4+...+n(n+1)
=>3S=1.2.3+2.3.3+3.4.3+...+n(n+1)3
=1.2.3+2.3.(4-1)+3.4(5-2)+...+n.(n+1)[(n+2)-(n-1)]
=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+n(n+1)(n+2)-(n-1)n(n+1)
=n(n+1)(n+2)
\(\Rightarrow S=\frac{n\left(n+1\right)\left(n+2\right)}{3}\)
