令6时x分，时针与分针夹角90°：30° * （6+x/60) - 6°*x = ± 90°180 + 1/2x - 6x = ± 90360 - 11x = ± 18011x=360±180 = 180或540x=180/11，或540/11即，6时(180/11)分；或6时（540/11）分，时针与分针夹角90°
