Linear Algebra: UNIT I: Vector Spaces

Vector Spaces: Theorems Part 1

Important Theorems for Engineering Maths or Mathematics - Vector Spaces: Theorems Part 1

 

Theorem 1: (Cancellation Law for vector addition).

If x, y and z are vectors in a vector space V such that x+z = y+z then x=y.

Proof:

There exists a vector v in V such that z+v=0. (Property 4)

x=x+0 = x+(z+v) = (x + z) + v

 = (y + z)+v = y+ (z+v) = y + (0)= y..

 

Theorem 2

In any vector space V, the following statements are true:

(a) 0x=0 for each x V.

(b) (−a) x = −(ax) = a (−x) for each a F and each x V.

(c) a0 = 0 for each a F.

(d) ax = 0 either a = 0 or x = 0.

Proof:

(a) Let us consider x V and 0 F.

It follows that 0x + 0x = (0+0) x

 = 0x

= 0x + 0

= 0 + 0x      (Commutative law)

Hence

0x =0 by the above previous theorem.

(b) The vector − (ax) is the unique element of V such that ax + (−ax) = 0.

  ax + (− a) x = [a + (− a)] x

 = 0x

= 0

(c) a•0 = a0+ 0       (Additive identity)

= a0 + [a0+ (− a0)]         (Associative law)

= a(0+0) − a0         (Distributive law)

= a0 − a0         (Identity law)

= 0          (Inverse)

(d) If ax = 0 then a=0 or x=0.

Let us assume that ax=0 and a≠0 such that x=0. Since a F then a−1 F.

 ax = 0

 a‒1(ax) = a‒1(0)

 (a‒1a) x = 0

 1.x = 0

 x=0

 

Theorem 3

The vector 0 is unique. (ie) The identity is unique.

Proof:

Let x V and e, e' V

 x+e = V and x+e' = V

x+e = x+e'

 e = e'           (By cancellation law)

 

Theorem 4

The vector y is unique (ie) The inverse is unique

Proof:

Let x V and y, y' V

 x+y = 0 and x+y' = 0

x+y = x+y'

y=y'                (By cancellation law)

 

Linear Algebra: UNIT I: Vector Spaces : Tag: maths, mathematics : - Vector Spaces: Theorems Part 1


Linear Algebra: UNIT I: Vector Spaces



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