初二数学!先化简在求值

来源:学生作业帮助网 编辑:作业帮 时间:2017/06/27 08:14:27
初二数学!先化简在求值初二数学!先化简在求值 初二数学!先化简在求值=1/(x+1)-(x+3)/(x+1)(x-1)×(x-1)²/(x+3)(x+1)=1/(x+1)-(x-1

初二数学!先化简在求值
初二数学!先化简在求值

 

初二数学!先化简在求值
=1/(x+1) -(x+3)/(x+1)(x-1) ×(x-1)²/(x+3)(x+1)
=1/(x+1) -(x-1)/(x+1)²
=(x+1)/(x+1)²-(x-1)/(x+1)²
=[(x+1)-(x-1)]/(x+1)²
=2/(x+1)²
当x=-3时
原式=2/(-3+1)²=1/2

先乘除后加减,你之前做的顺序有问题
再有最后一个分式要记得因式分解啊

原式=1/(x+1)-(x+3)/(x+1)(x-1)*(x-1)²/(x+1)(x+3)
=(x+1)/(x+1)²-(x-1)/(x+1)²
=(x+1-x+1)/(x+1)²
=2/(x+1)²
=2/(-3+1)²
=1/2

点击[http://pinyin.cn/1ISnbyLoMWZ] 查看这张图片。[访问验证码是:919184请妥善保管]

1/(x+1)-(x+3)/(x^2-1)÷(x^2+4x+3)/(x^2-2x+1)
=1/(x+1)-(x+3)/(x^2-1)X(x-1)^2/(x+1)(x+3)
=1/(x+1)-(x-1)/(x+1)^2
=(x+1-x+1)/(x+1)^2
=2/(x+1)^2
X=-3
原式=1/2