当x=1/9,y=-3时,求下式的值. (X+Y^2)+(2X+1/1*2 Y^2)+(3X+1/2*3 Y^2)+..
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当x=1/9,y=-3时,求下式的值. (X+Y^2)+(2X+1/1*2 Y^2)+(3X+1/2*3 Y^2)+...+(9X+1/8*9 Y^2)
括号中的分母为 1*2 2*3 8*9,这道题很多人算错,麻烦给出解释,和正确答案,还有解题步骤,还可追加分数
括号中的分母为 1*2 2*3 8*9,这道题很多人算错,麻烦给出解释,和正确答案,还有解题步骤,还可追加分数
![当x=1/9,y=-3时,求下式的值. (X+Y^2)+(2X+1/1*2 Y^2)+(3X+1/2*3 Y^2)+..](/uploads/image/z/17974533-21-3.jpg?t=%E5%BD%93x%3D1%2F9%2Cy%3D-3%E6%97%B6%2C%E6%B1%82%E4%B8%8B%E5%BC%8F%E7%9A%84%E5%80%BC.+%28X%2BY%5E2%29%2B%282X%2B1%2F1%2A2+Y%5E2%29%2B%283X%2B1%2F2%2A3+Y%5E2%29%2B..)
(X+Y^2)+(2X+1/1*2 Y^2)+(3X+1/2*3 Y^2)+...+(9X+1/8*9 Y^2)
=(1+2+...+9)x+(y^2+y^2-1/2y^2+1/2y^2-1/3y^2+.+1/8y^2-1/9y^2)
=45x+2y^2-1/9y^2
=45x+17/9y^2
=45×(1/9)+17/9×(-3)²
=5+17
=22
=(1+2+...+9)x+(y^2+y^2-1/2y^2+1/2y^2-1/3y^2+.+1/8y^2-1/9y^2)
=45x+2y^2-1/9y^2
=45x+17/9y^2
=45×(1/9)+17/9×(-3)²
=5+17
=22
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