The function f (x) = | lgx |, has 0

The function f (x) = | lgx |, has 0

Solving the equation lgx + x = 3

In order to solve the exact number, we have to rely on the computer. Here we provide an estimation method, dichotomy
The equation is lgx = - x + 3;
Obviously, the solution of the equation is the intersection of F (x) = lgx and G (x) = - x + 3;
By the combination of number and shape, the sketch of F (x) = lgx and G (x) = - x + 3 is drawn, and the intersection point is on (1,3);
f(1)g(3)；
Narrow range: F (2)

The interval of solution of equation lgx − 1x = 0 is ()
A. （0，1）B. （1，2）C. （2，3）D. [1，4]

Let f (x) = 1 x-lgx, then f (1) = 1-0 ＞ 0, f (2) = 12-lg2 ＞ 0, f (3) = 13-lg3 ＜ 0, f (4) = 14-lg4 ＜ 0. The equation 1 x-lgx = 0 must have roots in the interval (2,3), so choose C