Hey there!
Let's look for some patterns here.
In the first triangle, we see that there are six dots in total.
In the second triangle, there are nine dots in total.
And, for the third one, we see that there are 12 dots in total.
So, we see that it is counting up by threes because there is one more added to each side.
This is an arithmetic sequence, which means that there is a pattern of adding or subtracting from a base over and over again. There is a specific formula for calculating a certain term in a sequence and you can find proofs of it out there on the internet, but here is the formula.
To find a certain number in a sequence (in our case, 200), you
STEP 1: Take that certain number and subtract 1
200-1=199
STEP 2: You multiply this by the common difference, which is what you add or subtract to make the series. Since we keep on adding 3, our common difference is 3.
199×3=597
STEP 3: You add the first term in the series. In our case, this is the number of dots on the first triangle, which is six.
597+6=603
Therefore, the total number of dots on the 200th triangle of this sequence is 603 dots.
Now you can find a certain term in an arithmetic sequence! Have a wonderful day! :D
