Which of the following is equivalent to 18 - √-25

a. 5i

b. 18-5i

c. 18+5i

d. 23

This number is in complex form. To simplify a number in complex form, you simplify the two parts (real and imaginary) separately. For the given number 18 - √-25, this is how we do it:

The real part "18" is already simplified, so we only have to deal with the imaginary part " √-25".

18 - √-25

To solve for the square root of - 25, we factor it out first before simplifying:

18 - √ (25) (-1)

18 - 5 √ (-1)

For imaginary numbers, √-1 = i. Using that relation, we can simplify it to:

18 - 5i, which matches with the answer in letter B.