 
 <prompt> Wetin be di inverse for 90? Based on di previous question, write one context wey contain di answer. E fit be 1 - 20 sentences. Context: <response>: For di example wey dey up, di identity and di rotations make up one subgroup R = {id, r1, r2, r3}, wey dey marked for red for di group table wey dey up: any two rotations wey dem combine still dey form rotation, and one rotation fit cancel out by (i.e. na inverse to) di other rotations wey dey 270° for 90°, 180° for 180°, and 90° for 270° (abeg note say rotation for di opposite direction no dey defined). Di subgroup test na one necessary and sufficient condition for one subset H of one group G to be one subgroup: e dey enough to check say g−1h ∈ H for all di elements g, h ∈ H. Knowing di subgroups dey important to understand di group as one whole.d[›] 