Answer:
69
Step-by-step explanation:
Hey there! To find the 20th term of arithmetic sequence, we can do by using general terms.
General Term - Arithmetic
[tex]\displaystyle \large{a_n = a_1 + (n-1)d}[/tex]
where a_n is nth term, a_1 is the first term and d is our common difference.
We know the first term which is 12 and we want to find the 20th term which is our desired term.
Hence, the equation is [tex]\displaystyle \large{a_{20} = 12+(20-1)d}[/tex]
However, we don’t know the value of d yet which is common difference. To find the common difference, we can do by subtracting next term with previous term.
15-12 = 3
18-15 = 3
21-18 = 3
If we keep doing it, we’ll always get 3. Therefore, 3 is our common difference.
[tex]\displaystyle \large{a_{20}=12+(19)3}\\\displaystyle \large{a_{20}=12+57}\\\displaystyle \large{a_{20}=69}[/tex]
Thus, the 20th term is 69.
If you have any questions, let me know through the comment!
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