Ta có : 1 + 3 + 5 + ... + (2n - 1) = 225
=> \(\left[\left(2n-1-1\right):2+1\right].\left(2n-1+1\right):2=225\)
=> \(n.n=225\)
\(\Rightarrow n^2=225\)
\(\Rightarrow n^2=15^2\)
=> n = 15
Vậy n = 15
Các câu hỏi tương tự
tim n thoa
a/1+2+3+4+...+n=4950
b/2+4+6+...+2n=210
c?1+3+5+...+(2n-1) = 225
Tim n thoa :
A)2+4+6+...+2n=210
B)1+3+5+...+(2n-1)=225
tìm n để :
25n+3 thoa man 53
3n +1 thoa man 11 - 2n
ai làm đúng mk tick 1 tick , nhanh lên nha !
1) tim so nguyen x thoa man
a) -1-2-3-4 -...-x= 1275
b) -1-3-5-...- ( 2n -1) =-225
c) 16n -20n -24n-...-40n-44n =4800
tim n thuoc z thoa man
3n-4 chia het cho 2n-1
CM với n thuoc n ta có
1/1*3+1/3*5+1/5*7+...+1/(2n+1)(2n+3)=n+1/2n+3
Tim so nguyen n thoa man 2n + 1 chia het co n - 2
thong cam nha!!!! >:(
Cau 1: Tim n biet : 5/8 + 5/24 + 5/48 + 5/80 + ... + 5/2n + 2 . 2n + 4 = 189/112
Cau 2 : Cho A = 1 + 1/1.2 + 1/1.2.3 + ... + 1/1.2.3...2014. So sanh A voi 2
Cau 3 : Tim n biet : 5/3 + 5/15 + 5/35 + 5/63 +...+ 5/2n + 1 . 2n + 3 = 172/69
Chung minh rằng: 1*3*5*...*(2n-1)/(n+1)(n+2)...*2n=1/2n