Why is \( (1 + \sqrt{-5}) \times (1 - \sqrt{-5}) \) Equal to 6?

[harrylentil]

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

 

[mfb]

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.

 

[harrylentil]

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

 

[mfb]

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.

 

[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?

 

[mfb]

Did you expand the expression?

 

[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)

 

[berkeman]

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)