... 49 (SGK-Tr22) Tính nhanh: a) 37, 5.6,5 -7, 5.3,4-6,6 .7, 5+3,5. 37, 5 = 37, 5(6,5+3,5) 7, 5(3,4 + 6,6) = 37, 5.10 7, 5.10 = 10( 37, 5 -7, 5) = 10.30 = 300 b) 45 2 + 40 2 15 2 +80 .45 = (45 2 + 2.45.40 + 40 ... (SGK-Tr21) Tính nhanh: a) 73 2 - 27 2 = (72 - 27) (73 + 27) = 46. 100 = 4600 b) 37 2 -13 2 = ( 37 - 13)( 37 + 13) = 24.50 = 1200 c) 2002 2 -2 2 =(2002-2)(2002+2) = 2000.2004 = 40 080 00 3. Bài 49 (SGK-Tr22) ... - 3) 2 = (x 2 2 ) 2 b) 9(x + 5) 2 (x + 7) 2 = [3(x + 5)] 2 (x + 7) 2 = [3(x + 5)- (x+ 7) ][3(x+5) +(x -7) ] = [3x + 15 x 7] [3x + 15 + x + 7] = (2x +8) (4x + 22) = 4(x + 4)(2x + 11) 3. Bài 3:...