是39.8^2-2x39.8x49.8+49.8^2=(39.8-49.9)^2=(-10)^2=100
39.8" - 2 X 39.8 X 49.8 + 49.8"= 49.8" - 2 X 49.8 X 39.8 + 39.8"= (49.8 - 39.8)"= 10"= 100
39.8^2-2x39.8x49.9+49.8^2因式分解(39.8-49.8)^2=10^2=100
