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JEE Main 20236 AprilEvening Shift
Exam
JEE Main
Year
2023
Date
6 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Matrices

JEE Main 2023 · 6 April · Evening Shift · Mathematics · Matrices

Let P be a square matrix such that P ^ 2 = I - P . For α, β, γ, ∈ ℕ...

Let PP be a square matrix such that P2=I−P{P}^{2} = I - P. For α,β,γ,δ∈N\alpha, \beta, \gamma, \delta \in \mathbb{N}, if Pα+Pβ=\gammal−29P{P}^{\alpha} + {P}^{\beta} = \gammal - 29P and Pα−Pβ=\deltal−13P{P}^{\alpha} - {P}^{\beta} = \deltal - 13P, then α+β+γ−δ\alpha + \beta + \gamma - \delta is equal to

Options

  1. A1818
  2. B4040
  3. C2222
  4. D2424

Correct answer

D. 2424

Step-by-step solution

Given,

PP be a square matrix such that P2=I−P{P}^{2} = I - P,

Now solving P2=I−P{P}^{2} = I - P we get,

⇒P4=(I−P)(I−P)⇒ {P}^{4} = \left(I - P\right)\left(I - P\right)

⇒P4=I+P2−2P⇒ {P}^{4} = I + {P}^{2} - 2P

⇒P4=I+I−P−2P=2I−3P⇒ {P}^{4} = I + I - P - 2P = 2I - 3P

Now solving, P4⋅P2=P6=2I−5P+3P2{P}^{4} \cdot {P}^{2} = {P}^{6} = 2I - 5P + 3{P}^{2}

⇒P6=2I−5P+3(I−P)=5I−8P⇒ {P}^{6} = 2I - 5P + 3\left(I - P\right) = 5I - 8P... \left(i\right)</p><p>Similarly</p><p>Similarly{P}^{8} = 13I - 21P...(ii)... \left(ii\right)

Now adding \left(ii\right) + \left(i\right) we get,

P8+P6=18I−29P{P}^{8} + {P}^{6} = 18I - 29P

Now subtracting \left(ii\right) - \left(i\right) we get,

P8−P6=8I−13P{P}^{8} - {P}^{6} = 8I - 13P

Now comparing with Pα−Pβ=\deltal−13P{P}^{\alpha} - {P}^{\beta} = \deltal - 13P\text{and } {P}^{\alpha} + {P}^{\beta} = \gammal - 29P we get,

α=8,β=6,γ=18,δ=8\alpha = 8, \beta = 6, \gamma = 18, \delta = 8

Hence, α+β+γ−δ=8+6+18−8=24\alpha + \beta + \gamma - \delta = 8 + 6 + 18 - 8 = 24

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