x^2-16x-21

Question

how would this be factored?

 

Answer 1

That equation cannot be factored, since the solutions for x will not be whole numbers (they are actually irrational numbers).

If you use the quadratic formula instead, you should find that (after some simplification) x=8±√85

Answer 2

This quadratic expression is not factorable in rational domain, but factorable in irrational domain. You can get it by compeleting the square:

x²-16x-21 = x²-16x+8² - 8²-21 = (x-8)² - 85 = (x-8+√85)(x-8-√85)

 

Answer 3

For reference, the quadratic formula is x = (-b ± √(b² - 4ac))/2a, where (in this case)

a = 1
b = -16
c = -21