问两道关于代数式加减的两道题(七年级)1.化简:(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),并求当x=2,y=9时的值.(要有过程)(本题位置:配套青岛版七年级上册练习册 泰山出版社49页)2.求代
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![问两道关于代数式加减的两道题(七年级)1.化简:(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),并求当x=2,y=9时的值.(要有过程)(本题位置:配套青岛版七年级上册练习册 泰山出版社49页)2.求代](/uploads/image/z/11668591-55-1.jpg?t=%E9%97%AE%E4%B8%A4%E9%81%93%E5%85%B3%E4%BA%8E%E4%BB%A3%E6%95%B0%E5%BC%8F%E5%8A%A0%E5%87%8F%E7%9A%84%E4%B8%A4%E9%81%93%E9%A2%98%EF%BC%88%E4%B8%83%E5%B9%B4%E7%BA%A7%EF%BC%891.%E5%8C%96%E7%AE%80%EF%BC%9A%EF%BC%88x%2By%29%2B%282x%2By%2F1%2A2%29%2B%283x%2By%2F2%2A3%29%2B%E2%80%A6%2B%289x%2By%2F8%2A9%EF%BC%89%2C%E5%B9%B6%E6%B1%82%E5%BD%93x%3D2%2Cy%3D9%E6%97%B6%E7%9A%84%E5%80%BC.%EF%BC%88%E8%A6%81%E6%9C%89%E8%BF%87%E7%A8%8B%EF%BC%89%EF%BC%88%E6%9C%AC%E9%A2%98%E4%BD%8D%E7%BD%AE%EF%BC%9A%E9%85%8D%E5%A5%97%E9%9D%92%E5%B2%9B%E7%89%88%E4%B8%83%E5%B9%B4%E7%BA%A7%E4%B8%8A%E5%86%8C%E7%BB%83%E4%B9%A0%E5%86%8C+%E6%B3%B0%E5%B1%B1%E5%87%BA%E7%89%88%E7%A4%BE49%E9%A1%B5%EF%BC%892.%E6%B1%82%E4%BB%A3)
问两道关于代数式加减的两道题(七年级)1.化简:(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),并求当x=2,y=9时的值.(要有过程)(本题位置:配套青岛版七年级上册练习册 泰山出版社49页)2.求代
问两道关于代数式加减的两道题(七年级)
1.化简:(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),并求当x=2,y=9时的值.(要有过程)(本题位置:配套青岛版七年级上册练习册 泰山出版社49页)
2.求代数式a-(a+b)+(a+2b)-(a+3b)+...-(a+101b)的值,其中a=1/2,b=-( 1/3).(本题位置:配套青岛版七年级上册练习册 泰山出版社51页).
问两道关于代数式加减的两道题(七年级)1.化简:(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),并求当x=2,y=9时的值.(要有过程)(本题位置:配套青岛版七年级上册练习册 泰山出版社49页)2.求代
(1)(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9)
=(x+2x+3x+...+9x)+(y+y-y/2+y/2-y/3+y/3-y/4+...+y/8-y/9)
=45x+17y/9;
x=2,y=9时,原式=45*2+17*9/9=90+17=107
(2)a-(a+b)+(a+2b)-(a+3b)+...-(a+101b)
=(a-a-b)+(a+2b-a-3b)+...+(a+100b-a-101b)
=-b+(-b)+...+(-b)
=-51b
当a=1/2,b=-1/3时,原式=-51*(-1/3)=17
1.化简:(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),并求当x=2,y=9时的值.
(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),
=x+y+2x+y/1*2+3x+y/2*3+.......+9x+y/8*9
=45x+y(1/1*2+1/2*3+1/3*4+.....1/8*9)
=45x...
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1.化简:(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),并求当x=2,y=9时的值.
(x+y)+(2x+y/1*2)+(3x+y/2*3)+…+(9x+y/8*9),
=x+y+2x+y/1*2+3x+y/2*3+.......+9x+y/8*9
=45x+y(1/1*2+1/2*3+1/3*4+.....1/8*9)
=45x+y(1-1/2+1/2-1/3+1/3-1/4+1/4-.....-1/8+1/8-1/9)
=45x+y(1-1/9)
=45x+8y/9 当x=2,y=9时
=45*2+8*9/9
=90+8
=98
2.求代数式a-(a+b)+(a+2b)-(a+3b)+...-(a+101b)的值,其中a=1/2,b=-( 1/3).
a-(a+b)+(a+2b)-(a+3b)+.....-(a+101b)
=a-a-b+a+2b-a-3b+a+4b-........-a-101b
=-a+49b a=1/2,b=-( 1/3).
=-1/2-49/3
=-3/6-98/6
=-101/6
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