第一题2log(x- 7)- log(x-16) = 2 x等于17 和97

题目

第一题2log(x- 7)- log(x-16) = 2 x等于17 和97
第二题log3x- log 根号16 - x根号 =1 x等于 80/9 16-x是根号
第三题方程组 ( 2x-3/3) - y =-19/3
3x-2+( y-1/5)= 2 x=-6/5 y= 2/5
第四题 根号(x+2) - 根号(x-6) -2=0 x等于1分之9
第二题是log3x-log√(16-x)=1 x等于 80/9
第三题是方程组 ((2x-3)/3) - y =- 19/3
( 3x-2)+(y-1)/5=2

答案

1) log[(x-7)^2/(x-16)] = 2
=> (x-7)^2/(x-16) = 100
=> x^2 - 14x +49 = 100x -1600
=> x^2 -114x + 1649 = 0
=> (x-17)(x-97) = 0
=> x = 17 or x = 97
2 两边同乘2
log [(3x)^2/(16-x)] =2
=> 9x^2 = 100(16-x)
=> 9x^2 +100x - 1600 = 0
=> (9x -80)(x + 20) = 0
=> x = 80/9,(x = -20不成立）
3
(1) => 2/3 *x -1 - y =- 19/3
(2) => 15x - 10 + y -1 = 10
(1) + (2) => 47/3 * x -12 = 11/3 => x = 1
代入 （1） => y = 6
4 后两项移到等式右边,同平方
=》x+2 = x-6 + 4 + 4*(x-6)^(1/2)
=》 x-6 = 1
=> x = 7