# B Help me understand a simple calculation

1. Mar 4, 2017

### harrylentil

Why is (1 + sqrt(-5) x (1 – sqrt(-5)) equal to 6?

2. Mar 4, 2017

### Staff: Mentor

Did you expand the expression?

Do you know about imaginary numbers? You don't have to to calculate the expression, but it helps understanding what is going on.

3. Mar 4, 2017

### harrylentil

I don't know how to work with imaginary numbers.

4. Mar 4, 2017

### Staff: Mentor

Then just imagine that sqrt(-5) is some number that you don't know. You don't have to use imaginary numbers to solve the problem.

5. Mar 4, 2017

### harrylentil

Typo in my original question - a right bracket is missing. It should be,
Why is (1 + sqrt(-5)) x (1 – sqrt(-5)) equal to 6?

Anyone?

6. Mar 4, 2017

7. Mar 4, 2017

### JuanC97

You just have a difference of squares: (a+b)(a-b) = a^2-b^2 which, in your case means: (1 + sqrt(-5)) (1 – sqrt(-5)) = 1 - (-5)

8. Mar 4, 2017

### Staff: Mentor

Since Juan has shown the OP how to do this, and the OP keeps refusing to show any effort, this thread is now closed (after some cleanup)