数学
运用乘法公式计算: 1.(3x-5)的平方-(2x+7)的平方=_____________ 2.5x的平方(x+1)(x-1)=_______________
(3x-5)^2-(2x+7)^2 =[(3x-5)-(2x+7)][(3x-5)+(2x+7)] =(x-12)(5x+2) =5x^2-58x-24 5x^2(x+1)(x-1) =5x^2(x^2-1) =5x^4-5x^2
解: (1)(3x-5)^2-(2x+7)^2 =[(3x-5)+(2x+7)][(3x-5)-(2x+7)] =(5x+2)(x-12) (2)题目好象少了一个运算符.有几种可能: 5x^2+(x+1)(x-1) =5x^2+x^2-1 =6x^2-1 或5x^2-(x+1)(x-1) =5x^2-(x^2-1) =4x^2+1
答:(a+2b-1)^2 =a^2+2*a*(2b-1)+(2b-1)^2 =a^2+4ab-2a+4b^2-4b+1 =a^2+4b^2+4ab-2a-4b+1 ...详情>>
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