1)
Let ( 2 − i ) = a + b i \sqrt{(2-i)}=a+bi ( 2 − i ) = a + bi where a , b ∈ R a,b\in\R a , b ∈ R
2 − i = a 2 − b 2 + 2 2-i=a^2-b^2+2 2 − i = a 2 − b 2 + 2 abi
a 2 − b 2 = 2 a^2-b^2=2 a 2 − b 2 = 2 and 2 a b = − 1 2ab=-1 2 ab = − 1 ⟹ b = − 1 2 a \implies\>b=\frac{-1}{2a} ⟹ b = 2 a − 1
a 2 − ( − 1 2 a ) 2 = 2 ⟹ 4 a 4 − 8 a 2 − 1 = 0 a^2-(\frac{-1}{2a})^2=2\implies4a^4-8a^2-1=0 a 2 − ( 2 a − 1 ) 2 = 2 ⟹ 4 a 4 − 8 a 2 − 1 = 0
a 2 = 8 − + 64 + 16 8 a^2=\frac{8^+_-\sqrt{64+16}}{8} a 2 = 8 8 − + 64 + 16 But a ∈ R a\in\R a ∈ R
∴ a 2 = 2.118 \therefore\>a^2=2.118 ∴ a 2 = 2.118
a = − + 1.4553 a=^+_-1.4553 a = − + 1.4553
b = − 1 2 a = − + 0.3436 b=\frac{-1}{2a}=^+_-0.3436 b = 2 a − 1 = − + 0.3436
2 − i = − + ( 1.4553 − 0.3436 i ) \sqrt{2-i}=^+_-(1.4553-0.3436i) 2 − i = − + ( 1.4553 − 0.3436 i )
2)
A = ( 5 − 3 − 6 2 ) A=\begin{pmatrix}
5 & -3 \\
-6 & 2
\end{pmatrix} A = ( 5 − 6 − 3 2 )
Characteristic polynomial
P ( t ) = d e t ( A − t I ) = ( 5 − t − 3 − 6 2 − t ) P(t)=det(A-tI)=\begin{pmatrix}
5-t&-3 \\
-6&2-t
\end{pmatrix} P ( t ) = d e t ( A − t I ) = ( 5 − t − 6 − 3 2 − t )
= ( 5 − t ) ( 2 − t ) − 18 =(5-t)(2-t)-18 = ( 5 − t ) ( 2 − t ) − 18
= t 2 − 7 t − 8 =t^2-7t-8 = t 2 − 7 t − 8
Solving t 2 − 7 t − 8 = 0 , t = 8 o r − 1 t^2-7t-8=0\>,t=8 \>or-1 t 2 − 7 t − 8 = 0 , t = 8 or − 1
Eigenvalues are λ = 8 λ = − 1 \lambda=8\>\>\>\>\>\lambda=-1 λ = 8 λ = − 1
For ( A − 8 ) x = 0 (A-8)x=0 ( A − 8 ) x = 0
A − 8 = ( − 3 − 3 − 6 − 6 ) A-8=\begin{pmatrix}
-3 & -3 \\
-6& -6
\end{pmatrix} A − 8 = ( − 3 − 6 − 3 − 6 ) → t h e n − 1 3 R 1 R 2 − 2 R 1 \to^{R_2-2R_1}_{then\>\frac{-1}{3}R_1} → t h e n 3 − 1 R 1 R 2 − 2 R 1 ( 1 1 0 0 ) \begin{pmatrix}
1 & 1\\
0& 0
\end{pmatrix} ( 1 0 1 0 )
x 1 = − x 2 x_1=-x_2 x 1 = − x 2
Eigen vector = ( − 1 1 ) =\begin{pmatrix}
-1 \\
1
\end{pmatrix} = ( − 1 1 )
For ( A + 1 ) x = 0 (A+1)x=0 ( A + 1 ) x = 0
A + 1 = ( 6 − 3 − 6 3 ) → T h e n 1 3 R 1 R 2 + R 1 ( 2 − 1 0 0 ) A+1=\begin{pmatrix}
6 & -3\\
-6& 3
\end{pmatrix}\to^{R_2+R_1}_{Then\>\frac{1}{3}R_1}\begin{pmatrix}
2 & -1 \\
0 & 0
\end{pmatrix} A + 1 = ( 6 − 6 − 3 3 ) → T h e n 3 1 R 1 R 2 + R 1 ( 2 0 − 1 0 )
2 x 1 = x 2 2x_1=x_2 2 x 1 = x 2
Eigenvector = ( 1 2 ) \begin{pmatrix}
1 \\
2
\end{pmatrix} ( 1 2 )
P = ( − 1 1 1 2 ) P=\begin{pmatrix}
-1 & 1\\
1 & 2
\end{pmatrix} P = ( − 1 1 1 2 )
3)
The zero of R \R R is defined as
0 + 0 + a ( 0 ) ( 0 ) = 0 0+0+a(0)(0)=0 0 + 0 + a ( 0 ) ( 0 ) = 0
This shows that S S S is a subspace of R 2 \R^2 R 2 if and only b = 0 b=0 b = 0
Also S S S is a subspace of R 2 \R^2 R 2 if it is closed under addition and scalar multiplication
Let x 1 y 1 ∈ R 2 x_1y_1\in\R^2 x 1 y 1 ∈ R 2 and x 2 y 2 ∈ R 2 x_2y_2\in\R^2 x 2 y 2 ∈ R 2
( x 1 + y 1 ) , ( x 2 + y 2 ) : ( x 1 + y 1 ) + ( x 2 + y 2 ) + a ( x 1 + y 1 ) ( x 2 + y 2 ) = 0 (x_1+y_1),(x_2+y_2):(x_1+y_1)+(x_2+y_2)+a(x_1+y_1)(x_2+y_2)=0 ( x 1 + y 1 ) , ( x 2 + y 2 ) : ( x 1 + y 1 ) + ( x 2 + y 2 ) + a ( x 1 + y 1 ) ( x 2 + y 2 ) = 0
( x 1 y 1 ) + ( x 2 y 2 ) = x 1 + y 1 + a x 1 y 1 + x 2 + y 2 + a x 2 y 2 (x_1y_1)+(x_2y_2)=x_1+y_1+ax_1y_1+x_2+y_2+ax_2y_2 ( x 1 y 1 ) + ( x 2 y 2 ) = x 1 + y 1 + a x 1 y 1 + x 2 + y 2 + a x 2 y 2
= ( x 1 + y ) + ( y 1 + y 2 ) + a ( x 1 y 1 + x 2 y 2 ) =(x_1+y)+(y_1+y_2)+a(x_1y_1+x_2y_2) = ( x 1 + y ) + ( y 1 + y 2 ) + a ( x 1 y 1 + x 2 y 2 )
S S S is not a subspace of R 2 \R^2 R 2 unless a = 0 a=0 a = 0 b = 0 b=0 b = 0
Let α ∈ R \alpha\in\R α ∈ R
α ( x 1 y ) = α ( x + y + a x y ) \alpha(x_1y)=\alpha(x+y+axy) α ( x 1 y ) = α ( x + y + a x y )
= α x + x y + a α x y =\alpha\>x+xy+a\alpha\>xy = α x + x y + a α x y
α ( x ) x ( y ) = α x + α y + a α 2 x y \alpha(x)\>x(y)=\alpha\>x+\alpha\>y+a\alpha^2\>xy α ( x ) x ( y ) = α x + α y + a α 2 x y
S S S is not a subspace of R 2 \R^2 R 2 Unless a = 0 , b = 0 a=0,b=0 a = 0 , b = 0
4)
U = x ( 1 0 1 0 0 ) + y ( 0 1 1 0 2 ) + z ( 0 0 0 1 1 ) U=x\begin{pmatrix}
1 \\
0\\
1\\
0\\
0
\end{pmatrix}+y\begin{pmatrix}
0 \\
1 \\
1\\
0\\
2
\end{pmatrix}+z\begin{pmatrix}
0 \\
0 \\
0\\
1\\
1
\end{pmatrix} U = x ⎝ ⎛ 1 0 1 0 0 ⎠ ⎞ + y ⎝ ⎛ 0 1 1 0 2 ⎠ ⎞ + z ⎝ ⎛ 0 0 0 1 1 ⎠ ⎞
U U U is a subspace spanned by linearly independent set S = { ( 1 , 0 , 1 , 0 , 0 ) + ( 0 , 1 , 1 , 0 , 2 ) + ( 0 , 0 , 0 , 1 , 1 ) } S=\begin{Bmatrix}
( 1,0,1,0,0)+ (0,1,1,0,2)+(0,0,0,1,1)
\end{Bmatrix} S = { ( 1 , 0 , 1 , 0 , 0 ) + ( 0 , 1 , 1 , 0 , 2 ) + ( 0 , 0 , 0 , 1 , 1 ) }
By adjoining elements of F 5 F^5 F 5 that will not affect linear independence of
( 0 , 0 , 0 , 1 , 1 ) (0,0,0,1,1) ( 0 , 0 , 0 , 1 , 1 ) and ( 0 , 0 , 0 , 0 , 1 ) (0,0,0,0,1) ( 0 , 0 , 0 , 0 , 1 )
Span W
= = = { [ 0 0 0 1 1 ] \begin{bmatrix}
0 \\
0 \\
0\\
1\\
1
\end{bmatrix} ⎣ ⎡ 0 0 0 1 1 ⎦ ⎤ , [ 0 0 0 0 1 ] ,\begin{bmatrix}
0 \\
0 \\
0\\
0\\
1
\end{bmatrix} , ⎣ ⎡ 0 0 0 0 1 ⎦ ⎤ }
Or W = { ( 0 , 0 , 0 , x , x + y ) } W=\begin{Bmatrix}
(0,0,0,x,x+y)\\
\end{Bmatrix} W = { ( 0 , 0 , 0 , x , x + y ) }
Such that F 5 F^5 F 5 = u ⨁ w =u\bigoplus\>w = u ⨁ w
5)
The subset S S S of the vector space V V V is not a basis if
(i) S is linearly dependent
(ii) S is not a spanning set
Row echelon form of S is ( 2 0 0 0 7 2 0 0 0 − 5 t 7 + 15 7 ) \begin{pmatrix}
2&0&0 \\
0&\frac{7}{2}&0 \\
0&0&\frac{-5t}{7}\frac{+15}{7}
\end{pmatrix} ⎝ ⎛ 2 0 0 0 2 7 0 0 0 7 − 5 t 7 + 15 ⎠ ⎞
⟹ − 5 t 7 + 15 7 = 0 \implies\frac{-5t}{7}+\frac{15}{7}=0 ⟹ 7 − 5 t + 7 15 = 0
∴ t = 3 \therefore\>t=3 ∴ t = 3
The vectors are not basis of R 3 \R^3 R 3 if t ≠ 3 t\ne3 t = 3
Comments