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Metamath Proof Explorer

Theorem fsump1

Description: The addition of the next term in a finite sum of A ( k ) is the current term plus B i.e. A ( N + 1 ) . (Contributed by NM, 4-Nov-2005) (Revised by Mario Carneiro, 21-Apr-2014) (Proof shortened by SN, 22-Mar-2025)

Ref Expression
Hypotheses fsump1.1 ⊢ ( 𝜑 → 𝑁 ∈ ( ℤ≥ ‘ 𝑀 ) )
fsump1.2 ⊢ ( ( 𝜑 ∧ 𝑘 ∈ ( 𝑀 ... ( 𝑁 + 1 ) ) ) → 𝐴 ∈ ℂ )
fsump1.3 ⊢ ( 𝑘 = ( 𝑁 + 1 ) → 𝐴 = 𝐵 )
Assertion fsump1 ( 𝜑 → Σ 𝑘 ∈ ( 𝑀 ... ( 𝑁 + 1 ) ) 𝐴 = ( Σ 𝑘 ∈ ( 𝑀 ... 𝑁 ) 𝐴 + 𝐵 ) )

Proof

Step Hyp Ref Expression
1 fsump1.1 ⊢ ( 𝜑 → 𝑁 ∈ ( ℤ≥ ‘ 𝑀 ) )
2 fsump1.2 ⊢ ( ( 𝜑 ∧ 𝑘 ∈ ( 𝑀 ... ( 𝑁 + 1 ) ) ) → 𝐴 ∈ ℂ )
3 fsump1.3 ⊢ ( 𝑘 = ( 𝑁 + 1 ) → 𝐴 = 𝐵 )
4 peano2uz ⊢ ( 𝑁 ∈ ( ℤ≥ ‘ 𝑀 ) → ( 𝑁 + 1 ) ∈ ( ℤ≥ ‘ 𝑀 ) )
5 1 4 syl ⊢ ( 𝜑 → ( 𝑁 + 1 ) ∈ ( ℤ≥ ‘ 𝑀 ) )
6 5 2 3 fsumm1 ⊢ ( 𝜑 → Σ 𝑘 ∈ ( 𝑀 ... ( 𝑁 + 1 ) ) 𝐴 = ( Σ 𝑘 ∈ ( 𝑀 ... ( ( 𝑁 + 1 ) − 1 ) ) 𝐴 + 𝐵 ) )
7 eluzelz ⊢ ( 𝑁 ∈ ( ℤ≥ ‘ 𝑀 ) → 𝑁 ∈ ℤ )
8 1 7 syl ⊢ ( 𝜑 → 𝑁 ∈ ℤ )
9 8 zcnd ⊢ ( 𝜑 → 𝑁 ∈ ℂ )
10 1cnd ⊢ ( 𝜑 → 1 ∈ ℂ )
11 9 10 pncand ⊢ ( 𝜑 → ( ( 𝑁 + 1 ) − 1 ) = 𝑁 )
12 11 oveq2d ⊢ ( 𝜑 → ( 𝑀 ... ( ( 𝑁 + 1 ) − 1 ) ) = ( 𝑀 ... 𝑁 ) )
13 12 sumeq1d ⊢ ( 𝜑 → Σ 𝑘 ∈ ( 𝑀 ... ( ( 𝑁 + 1 ) − 1 ) ) 𝐴 = Σ 𝑘 ∈ ( 𝑀 ... 𝑁 ) 𝐴 )
14 13 oveq1d ⊢ ( 𝜑 → ( Σ 𝑘 ∈ ( 𝑀 ... ( ( 𝑁 + 1 ) − 1 ) ) 𝐴 + 𝐵 ) = ( Σ 𝑘 ∈ ( 𝑀 ... 𝑁 ) 𝐴 + 𝐵 ) )
15 6 14 eqtrd ⊢ ( 𝜑 → Σ 𝑘 ∈ ( 𝑀 ... ( 𝑁 + 1 ) ) 𝐴 = ( Σ 𝑘 ∈ ( 𝑀 ... 𝑁 ) 𝐴 + 𝐵 ) )