Can someone explain the snake method, I don't understand how to do it

x ∈ [−2; 1] ∪ 3.5

Step-by-step explanation:

Given

Inequality: (x-1)(x+2)(2x-7)≤0

Solution:

If we solve the corresponding equation (x-1)(x+2)(2x-7)²= 0, we get roots

x =  -2, 1, 3.5

We need to consider the following 4 intervals:

(−∞; −2), [−2; 1], (1; 3.5), (3.5; ∞)

1st interval (−∞; −2)

The expression (x-1)(x+2)(2x-7)² is positive as two of the multiples are negative and one is always positive (square number), and therefore  does not satisfy the inequality.

2nd interval  [−2; 1]

The expression is negative as only one of the multiples is negative, and therefore the interval (−1; 2) satisfies the inequality.

3rd interval (1; 3.5)

The expression is positive as all the multiples are positive. Therefore, the interval (1; 3.5) also does not satisfy the inequality.

4th interval

The expression is positive as above, and therefore also does not satisfy the inequality.  

So, the answer to the inequality is:

x ∈ [−2; 1] ∪ 3.5

If you make you answer for clear i can answer it : )