Question

What is the length (magnitude) of the vector (2,-1)?

a. √5
b. √2
c.-2
d.1

Answer 1

( 2, -1) refers to the x y, we can form a triangle and use the pythaogoros theorom

length = root ( x^2 + y^2)

= root(2^2 + -1^2)
= root ( 5 )

so the answer is A

Answer 2

use \[a^2=b^2+c^2\] so \[a^2 = \pm\sqrt{2^2+1^1} = \pm\sqrt{5}\]

Answer 3

so the answer is a