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Exercise 1.10. Verify that with 
sigma=(12),tau=(123), the standard representation las a basis 
alpha=(omega,1,omega^(2)),beta=(1,omega,omega^(2)), with

tau alpha=omega alpha,quad tau beta=omega^(2)beta,quad sigma alpha=beta,quad sigma beta=alpha.

Verify that with σ=(12)\sigma=(1\,2), τ=(123)\tau=(1\,2\,3), the standard representation l as a basis α=(ω,1,ω2)\alpha=(\omega,1,\omega^{2}), β=(1,ω,ω2)\beta=(1,\omega,\omega^{2}), with τα=ωα\tau \alpha=\omega \alpha, τβ=ω2β\tau \beta=\omega^{2}\beta, σα=β\sigma \alpha=\beta, σβ=α\sigma \beta=\alpha.

Full solution

Q. Verify that with σ=(12)\sigma=(1\,2), τ=(123)\tau=(1\,2\,3), the standard representation l as a basis α=(ω,1,ω2)\alpha=(\omega,1,\omega^{2}), β=(1,ω,ω2)\beta=(1,\omega,\omega^{2}), with τα=ωα\tau \alpha=\omega \alpha, τβ=ω2β\tau \beta=\omega^{2}\beta, σα=β\sigma \alpha=\beta, σβ=α\sigma \beta=\alpha.
  1. Define permutations σ\sigma and τ\tau: First, let's define the permutations σ\sigma and τ\tau. σ\sigma is the permutation (12)(1 2), which swaps the first and second elements, and τ\tau is the permutation (123)(1 2 3), which cycles the first element to the second position, the second to the third, and the third to the first.
  2. Define basis vectors α\alpha and β\beta: Next, we define the basis vectors α\alpha and β\beta. α\alpha is given by (ω,1,ω2)(\omega, 1, \omega^2), and β\beta is given by (1,ω,ω2)(1, \omega, \omega^2), where ω\omega is a complex cube root of unity, meaning ω3=1\omega^3 = 1 and β\beta00.
  3. Verify action of tau on alpha: We need to verify the action of τ\tau on α\alpha. Since τ\tau is the cycle (123)(123), applying τ\tau to α\alpha gives us (1,ω2,ω)(1, \omega^2, \omega). We know that ωα=(ω2,ω,1)\omega \cdot \alpha = (\omega^2, \omega, 1), which is the same as the result of applying τ\tau to α\alpha. Therefore, α\alpha00.
  4. Verify action of tau on beta: Now, we verify the action of tau on beta. Applying tau to beta gives us (ω,ω2,1)(\omega, \omega^2, 1). Multiplying beta by ω2\omega^2 gives us (ω2,1,ω)(\omega^2, 1, \omega), which is the same as the result of applying tau to beta. Therefore, τβ=ω2β\tau \beta = \omega^2 \beta.
  5. Verify action of sigma on alpha: Next, we verify the action of sigma on alpha. Sigma swaps the first and second elements, so applying sigma to alpha gives us (1,ω,ω2)(1, \omega, \omega^2), which is exactly beta. Therefore, σα=β\sigma \alpha = \beta.
  6. Verify action of sigma on beta: Finally, we verify the action of sigma on beta. Applying sigma to beta swaps the first and second elements, resulting in (ω,1,ω2)(\omega, 1, \omega^2), which is exactly alpha. Therefore, σβ=α\sigma \beta = \alpha.

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