Question

While attempting to multiply the expression (2-5i)(5+2i) a student made a mistake.

Answer 1

Answer:

The left side of the equation is ignored

i is treated as -1, which it is not, it is instead the square root of negative 1.

To solve it properly we get:

(2 - 5i)(5 + 2i)

= 10 + 4i - 25i - 10i²

= 10 + 21i + 10

= 20 - 21i

Answer 2

Answer:

The error is that, the student replaced i with -1 which is wrong as i = √-1

And he has replaced i^2 with 1 while i^2 = -1

Step-by-step explanation:

Given two numbers that are being multiplied are:

(2-5i)(5+2i)

We will solve the question to get the right result so that the error can be detected.

So, multiplying both

$= 2(5+2i)-5i(5+2i)\\=10+4i-25i-10i^2\\=10-21i-10(-1)\ \ \ as\ i^2 = -1\\=10-21i+10$

The error is that, the student replaced i with -1 which is wrong as i = √-1

And he has replaced i^2 with 1 while i^2 = -1