(-k/2)^2=2*18,k^2=36*4.How is this possible i have no idea where *4 came from

Answer 1

( - k / 2 )² = k² / 4

So:

( - k / 2 )² = 2 ∙ 18

k² / 4 = 36

Multiply both sides by 4

k² = 36 ∙ 4

k² = 144

k = ± √144

k = ± √12

Answer 2

My typo.

Final solution:

k = ± 12

Answer 3

Thanks alot