五 生活中的多边形多边形的面积(信息窗2)等式的性质1.根据等式的性质,填一填。(1) x + 80 = 120 x + 80 - 80 = 120 (2) 45 + x = 96 45 + x - 45 = 96 2.根据等式的性质,填一填。(1) x - 80 = 120 x - 80 + 80 = 120 (2) x - 5.8 = 12 x -5.8 + 5.8 = 12 3.判断下面等式是否成立,成立的打“”。(1) y - 80 = 200 y - 80 + 80 = 200 -80 ( )(2) x + 5.8 = 12.8 x +5.8 - 5.8 = 12.8 - 12.8 ( )(3) 18 + x = 25.5 18 + x - 18 = 25.5 - 18 ( )4.根据等式的性质,填一填。如果A=B,那么A - 2 = B A + c = B A = B + 6 A = B D参考答案:1. (1)-80 (2)-452. (1)+ 80 (2)+5.83. (3)4. (1)- 2 (2)+ c (3)+ 6 (4)- D