Final answer:
The 18th word in the pattern 'Circle square circle triangle circle rectangle' is 'rectangle', because 18 is a multiple of the number of words in one cycle of the pattern (6), which means the pattern would have completed exactly 3 full cycles by this point.
Step-by-step explanation:
To determine the 18th word in the given pattern, we first need to recognize the sequence.
The pattern is 'Circle square circle triangle circle rectangle', which contains six words.
Since we are looking for the 18th element, we divide the position number (18) by the number of elements in the pattern (6).
This gives us 18 ÷ 6 = 3 full cycles of the pattern, with no remainder.
Therefore, the 18th word is the same as the 6th word of the pattern because 18 is a multiple of 6.
Given this, the 18th word in the pattern is 'rectangle'.