I ran your question against a Google AI w image recognition. Here is the full explanation https://poe.com/s/xdXDUYU2cjl1myfpxOua
tl/dr λ₁ in the Numerator: The key point is that the final expression involves a product. While each individual integral resulted in λᵢ in the numerator, the product includes the term from i=2. This term has λ₂ in the numerator and (λ₁ + λ₂) in the denominator.
Therefore, the final expression does indeed have λ₁ in the numerator, but it comes from the (i=2) term in the product, not from the integration of a single term.
Rupa Akter You are absolutely correct (I have no idea what the AI is yapping about), the final integral has lambda_i in the numerator. It's either a typo or an incorrect "relabeling".