a,S=1.2+1.3+3.4+…+(n-1).n b,S=1.2.3+2.3.4+3.4.5+…+(n-2)(n-1)n 21/07/2021 Bởi Genesis a,S=1.2+1.3+3.4+…+(n-1).n b,S=1.2.3+2.3.4+3.4.5+…+(n-2)(n-1)n
S=1.2+1.3+3.4+…+(n-1).n 3S = 1.2.3 + 2.3.3 + 3.4.3 + … + (n – 1).3n 3S = 1.2.3 + 2.3.(4 – 1) + 3.4.(5 – 2) + … + (n – 1).n.[(n + 1) – (n – 2)] 3S = 1.2.3 + 2.3.4 – 1.2.3 + 3.4.5 – 2.3.4 + … + (n – 1).n.(n + 1) – (n – 2)(n – 1).n 3S = n(n + 1)(n – 1) S=[ n.(n + 1)(n – 1)] :3 Bình luận
Đáp án: Giải thích các bước giải: S=1.2+1.3+3.4+…+(n-1).n 3S = 3.[ 1.2 + 2.3 + 3.4 + … + (n – 1).n] 3S = 1.2.3 + 2.3.3 + 3.4.3 + … + (n – 1).n.3 3S = 1.2.3 + 2.3.(4 – 1) + 3.4.(5 – 2) + … + (n – 1).n.[(n + 1) – (n – 2)] 3S = 1.2.3 + 2.3.4 – 1.2.3 + 3.4.5 – 2.3.4 + … + (n – 1).n.(n + 1) – (n – 2)(n – 1).n 3S = (n – 1)n(n + 1) S= (n – 1).n.(n + 1) : 3. Bình luận
S=1.2+1.3+3.4+…+(n-1).n
3S = 1.2.3 + 2.3.3 + 3.4.3 + … + (n – 1).3n
3S = 1.2.3 + 2.3.(4 – 1) + 3.4.(5 – 2) + … + (n – 1).n.[(n + 1) – (n – 2)]
3S = 1.2.3 + 2.3.4 – 1.2.3 + 3.4.5 – 2.3.4 + … + (n – 1).n.(n + 1) – (n – 2)(n – 1).n
3S = n(n + 1)(n – 1)
S=[ n.(n + 1)(n – 1)] :3
Đáp án:
Giải thích các bước giải:
S=1.2+1.3+3.4+…+(n-1).n
3S = 3.[ 1.2 + 2.3 + 3.4 + … + (n – 1).n]
3S = 1.2.3 + 2.3.3 + 3.4.3 + … + (n – 1).n.3
3S = 1.2.3 + 2.3.(4 – 1) + 3.4.(5 – 2) + … + (n – 1).n.[(n + 1) – (n – 2)]
3S = 1.2.3 + 2.3.4 – 1.2.3 + 3.4.5 – 2.3.4 + … + (n – 1).n.(n + 1) – (n – 2)(n – 1).n
3S = (n – 1)n(n + 1)
S= (n – 1).n.(n + 1) : 3.