Arithmetic series practice
For the arithmetic sequence \(-13, -9, -5, \ldots\), find \(d\) and calculate \(S_{20}\).
Worked practice: sequences and series
Find the common change or ratio, then use it to calculate the requested term or sum.
Write a full answer
Now write the response in full, in your own words — this is what the exam asks for. The AI marks it on the same moves you built above (focus, evidence, technique, judgement) and gives feedback on reasoning, evidence, and expression.