复习 (19 16:36:10)1. a<3,则不等式(a-3)x<a-3的解集是__________.2. 若2x2-3xy-20y2=0,且y≠0,则x/y=__________.
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![复习 (19 16:36:10)1. a<3,则不等式(a-3)x<a-3的解集是__________.2. 若2x2-3xy-20y2=0,且y≠0,则x/y=__________.](/uploads/image/z/755910-54-0.jpg?t=%E5%A4%8D%E4%B9%A0+%2819+16%3A36%3A10%291.%26%23160%3B%26%23160%3B%26%23160%3B%26%23160%3B%26%23160%3B%26%23160%3B+a%EF%BC%9C3%2C%E5%88%99%E4%B8%8D%E7%AD%89%E5%BC%8F%EF%BC%88a-3%EF%BC%89x%EF%BC%9Ca-3%E7%9A%84%E8%A7%A3%E9%9B%86%E6%98%AF__________.2.%26%23160%3B%26%23160%3B%26%23160%3B%26%23160%3B%26%23160%3B%26%23160%3B+%E8%8B%A52x2-3xy-20y2%3D0%2C%E4%B8%94y%E2%89%A00%2C%E5%88%99x%2Fy%3D__________.%26%23160%3B)
复习 (19 16:36:10)1. a<3,则不等式(a-3)x<a-3的解集是__________.2. 若2x2-3xy-20y2=0,且y≠0,则x/y=__________.
复习 (19 16:36:10)
1. a<3,则不等式(a-3)x<a-3的解集是__________.
2. 若2x2-3xy-20y2=0,且y≠0,则x/y=__________.
复习 (19 16:36:10)1. a<3,则不等式(a-3)x<a-3的解集是__________.2. 若2x2-3xy-20y2=0,且y≠0,则x/y=__________.
1).由于a<3,
所以a-3<0,
于是不等式(a-3)x<a-3两边同除以a-3(除数为负数,不等号方向改变)
得到,
x>1;
2).2x2-3xy-20y2=0
上式两边同除以y^2,得到
2(x/y)^2-3(x/y)-20=0
配方,得
(x/y)^2-3/2(x/y)-10=0
(x/y)^2-2*(x/y)*(3/4)+(3/4)^2-(3/4)^2-10=0
(x/y-3/4)^2=169/16
两边开跟,得
x/y-3/4=+13/4或者x/y-3/4=-13/4
所以,
x/y=4或者-5/2