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13+23+...+n3=n.(n+1).(2n+1);6
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tim x thuoc N biet 1/3+1/6+1/10...+1/x.(x+1) :2=2001/2003
tim x thuoc N biet
x+(x+1)+(x+2)+(x+3)+.......+(x+30)=1240
1+2+3+.....+x=210
tim x thuoc N biet 3x+2+3x+1+3x<1053
Tim x thuoc N biet
a)13 + 23 + 33 + ...+103 = (x +1)2
b)1+3+5+...+99=(x - 2)2
tim x thuoc N biet
a, 125.n=5^7
b, 2^3.n-3^4=2^5-5
c, (2^3+2) n+3^2.n.5-10=10^2
d, 5^n.5=125
e, 9 be hon hoac bang 3^n<90
f, (3n+1)^3=64
tim x thuoc N biet
a, 125.n=5^7
b, 2^3.n-3^4=2^5-5
c, (2^3+2) n+3^2.n.5-10=10^2
d, 5^n.5=125
e, 9 be hon hoac bang 3^n<90
f, (3n+1)^3=64
Tim x thuoc so nguyen,biet:
a. (x+1).(x-2)=0
b.10+3(x-1)=10+6x
c. x-96=(9443-x)-15
tim x thuoc N, biet [x-1] [x+3]=6
Tim x thuoc Z biet:
a,(10 - x)^2 / 3+3= -9
b,|x-6| *7-(-2)^2= -8+39