Linear Algebra: UNIT I: Vector Spaces

Linear span: Example Solved Problems

Important Example Solved Problems - Engineering Maths or Mathematics - Linear span: Example Solved Problems

Linear span

Example Problems

 

Example 12

Verify 2x3− 2x2[P (x)]+12x – 6 is a linear combination of x3− 2x2[Q(x)]−5x−3 and 3x3−5x2[R (x)]−4x−9 in P3 (R).

Solution:

Let v = av1+bv2

 2x3 − 2x2 + 12x − 6 = a (x3 − 2x2 − 5x − 3) + b (3x3 − 5x2 − 4x−9)

2x3− 2x2+12x−6=x3 (a + 3b) + x2 (−2a − 5b) + x (−5a−4b) + (− 3a − 9b)

Equating the co−efficients on both sides we get

a+3b=2          ...(1)

−2a−5b=−2       ...(2)

−5a−4b = 12       ...(3)

−3a−9b=−6   ...(4)

From (1) and (2); −2a−5b=−2

2a+6b = 4

 b = 2.

From (1); a +3 (2) = 2

a=2−6

 a=−4.

Equation − 5a−4b= 12 holds good.

−5(−4)−4 (2) = 12

  20−8= 12

Equation−3a−9b−6 is also satisfied.

−3(−4) − 9(2)=−6

12−18=−6

Hence 2x3− 2x2 + 12x−6 is a linear combination of x3−2x2−5x−3 and 3x3−5x−4x−9.

  P(x) is a linear combination of Q (x) and R (x).

 

Example 13

Verify 3x3 – 2x2 P(x) +7x+8 is a linear combination of x3−2x2 Q(x) −5x−3 and 3x3−5x2 R (x)−4x – 9 in P3 (R).

Solution:

Let v=av1+bv2

  3x3 −2x2+7x+8 = a (x3 − 2x2 − 5x − 3) + b (3x3 – 5x2 − 4x − 9)

 3x3− 2x2+7x+8 = x3(a + 3b) + x2(− 2a − 5b) + x(− 5a − 4b) + (− 3a − 9b)

Equating the coefficients on both sides, we get

 a+3b=3    ...(1)

2a−5b=−2     ...(2)

−5a−4b=7    ...(3)

−3a−9b=8      ...(4)

From (2) and (1);

− 2a − 5b = − 2

2a+6b=6

:. b = 4.

From (1):

a+12=3

  a=−9.

From (3): −5(−9)−4(4)=7

45−16 ≠ 7 and also

From (4): −3(−9)−9 (4) ≠ 8

These two conditions are not satisfied.

Hence 3x2−2x2+7x+8 is not a linear combinations x3−2x2−5x−3 and 3x3−5x2−4x−9.

 P(x) is not a linear combination of Q (x) and R (x).

 

Example 14

Let S = { (1, 2), (2, 1) }; V=R2. Prove that it is a linear span.

Solution:

Let us consider (x, y) V

 (x, y) = α(1, 2) + β(2, 1) = (α, 2α)+(2β, β)

(x, y) = (α + 2β, 2α+β)

 α + 2β = x ... (1)

2α + β = y


From equation (2);

 β = 2x−y

 2α = y – ( (2x– y) / 3 )

2α = [ 3y – 2x + y ] / 3

2α = (4y−2x) / 3

α = (2y−x) / 3

(x, y) = ( 2y−x / 3 )(2, 1) + ( 2x−y / 3 )(2, 1)

 (x, y) is a linear combination of S

  (x, y) L (S)

VL(S) and L (S)V

L(S) = V.

 

Linear Algebra: UNIT I: Vector Spaces : Tag: maths, mathematics : - Linear span: Example Solved Problems


Linear Algebra: UNIT I: Vector Spaces



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