Not really imagery, but characters. I personify almost everything. I can depict them, but I also imagine little stories about them.
Mr. Sine and Mrs. Cosine did a contest to determine who would appear in the Simpson formulas. The first round was about the sum of two sines. Mr. Sine is a calm, steady person. He knew there would be more rounds. He didn't go to deep, that's why there is a cosine too in the formula. But he still won the round, that's why he gets the plus sign:
sin(a)+sin(b) = sin((a+b)/2)cos((a-b)/2).
The second round was about the difference of two sines. Sine had a disadvantage because of the minus sign. Cosine won the round with a small difference.
sin(a)-sin(b) = sin((a-b)/2)cos((a+b)/2).
The third round was about the sum of two cosines. Cosine wanted to win this round so badly she really went to the limits of her power. She won with a big difference:
cos(a)+cos(b) = cos((a+b)/2)cos((a-b)/2)
Because Cosine had used everything she had in the third round, there was nothing left for the fourth. She only could make her presence felt with an overall minus sign.
cos(a)-cos(b) = -sin((a+b)/2)sin((a-b)/2).