а₁ = 10, a, 19.

It looks like you're listing elements of a sequence with a specific pattern, but the sequence isn't completely defined with the information provided. You've given the first term (a₁ = 10) and the third term (a₃ = 19), but the second term is simply listed as "a," which appears to be a placeholder for the actual value.

To find the pattern of the sequence and to determine the missing second term (a₂), we will need more information. If the sequence is arithmetic, that means there is a constant difference between the terms. If it is geometric, there is a constant ratio between the terms.

However, if we assume it is an arithmetic sequence (which is a common type of sequence in these cases), we can find the common difference by subtracting the first term from the third term and dividing by 2 because the third term is obtained by adding the common difference twice to the first term.

Let's try to find the common difference (d): a₃ = a₁ + 2d 19 = 10 + 2d 19 - 10 = 2d 9 = 2d d = 9/2 d = 4.5

Now that we have the common difference, we can find the second term: a₂ = a₁ + d a₂ = 10 + 4.5 a₂ = 14.5

So, the first three terms of the sequence, assuming it's arithmetic, would be: a₁ = 10 a₂ = 14.5 a₃ = 19

Again, without additional context or information about the pattern of the sequence, we can't be certain this is the correct interpretation, but based on what is given, it's a reasonable assumption. If the sequence is not arithmetic, you'll need to provide further details on how the terms are related to each other.