Question

b^2-40<0 is
[b+(2square root 10)][b-(2square root ten)]

Could you explain how did it become like tat? Thks!

Answer 1

(x-y)(x+y) = x^2-y^2

you have
x = b
y = √40 = 2√10

so,

b^2-40 = (b+√40)(b-√40) = (b+2√10)(b-2√10)