Jest dany ciąg o wzorze: an=8n+5
Wyznacz S42
a1 = 8* 1 + 5 = 13a2 = 8*2 + 5 = 21 r = a2 - a1r = 21 - 13r = 8a₄₂ = 8 * 42 + 5 = 341S₄₂ = · nS₄₂ = · 42 S₄₂ = 7434
tj ciag arytmetyczny
a₁= 8·1+5= 13
a₂=8·2+5=21
a₂-a₁= 8=r
mozna udowodnic r
an+1 =8(n+1)+5=8n+8+5=8n+13
an+1 -an= (8n+13) -(8n+5)= 8n+13- 8n -5 =8
a₄₂=8·42+5=336+5=341
S₄₂=(a₁+a₄₂)·42
2
=(13+341)·21=354·21=7434
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a1 = 8* 1 + 5 = 13
a2 = 8*2 + 5 = 21
r = a2 - a1
r = 21 - 13
r = 8
a₄₂ = 8 * 42 + 5 = 341
S₄₂ = · n
S₄₂ = · 42
S₄₂ = 7434
tj ciag arytmetyczny
a₁= 8·1+5= 13
a₂=8·2+5=21
a₂-a₁= 8=r
mozna udowodnic r
an+1 =8(n+1)+5=8n+8+5=8n+13
an+1 -an= (8n+13) -(8n+5)= 8n+13- 8n -5 =8
a₄₂=8·42+5=336+5=341
S₄₂=(a₁+a₄₂)·42
2
=(13+341)·21=354·21=7434