Final answer:
The value of '[-5.8]' is determined by the floor function, which rounds the number down to the nearest whole integer. As -6 is the closest integer less than -5.8, the correct answer is D. -6.
Step-by-step explanation:
The question asks to select the value of '[-5.8]'. This is known as the floor function, which means we are looking for the greatest integer that is less than or equal to -5.8. Since -6 is less than -5.8 and is also an integer, the floor of -5.8 is -6. Therefore, the correct answer is D. -6.
It's important to understand that floor functions round the number down to the nearest whole number if the number is negative. It's essentially 'truncating down' the given number to its nearest whole integer in the negative direction on the number line. For instance, consider the following: the floor of -5.1, -5.2, or -5.9 would also be -6 because they all lie between -6 and -5 on the number line and we round down to the nearest integer.