... b) 3 – 3ab(a + b) = a 3 + 3a2b+ 3ab2+ b 3 –3a2b –3ab2 = a 3 + b 3 . Vậy :a 3 + b 3 = (a+b) 3 -3ab(a+b) b) (a – b) 3 + 3ab(a-b) = a 3 – 3a2b +3ab2 – b2 = a 3 - b 3 ... xéta) 37 ,5.6,5-7,5 .3, 4 - 6,6.7,5 +3, 5 .37 ,5= (37 ,5.6,5 +3, 5 .37 ,5)-( 7,5 .3, 4+6,6.7,5) =37 ,5(6,5 +3, 5)-7,5 (3, 4+6,6)= 37 ,5.10-7,5.10= 37 5 – 75 = 30 0- Các nhóm làm câu bb) 452+402-152 +80 .45= ... -4x -3 - 2x4 - 8x 3 - 6x2 2x2 -5x 3 +21x2 +11x -3 -5x 3 : x2 = -5x 2x4 -13x 3 +15x2+11x -3 x2-4x -3 - 2x4 - 8x 3 - 6x2 2x2-5x -5x 3 +21x2 +11x -3 - -5x 3 +20x2...