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Q.Consider the matrices P = [[3, -1, 2], [-2, 1, 4]], Q = [[4, -2, 1], [-5, 3, 1]] and R = [[3, 0, 0], [0, 3, 0], [0, 0, 3]].

(i) The order of the matrix PR is ______.
(1)
(ii) Show that PR = 3P.
(1)
(iii) Find 3P + Q. (1)
Kerala DhseKerala DHSE Plus Two Board 2026Subjective· 3mImportance★★★★★
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P is 2×3 and R is 3×3, so PR is 2×3; since R = 3I, multiplying any matrix by R just scales it by 3, giving PR = 3P directly.

  1. Order of PR. P has order 2×32\times 3 and R has order 3×33\times 3. For the product PR to be defined, the number of columns of P (3) must equal the number of rows of R (3) — it does. The product then has order (rows of P) × (columns of R) = 2×32\times 3.
  2. Show PR = 3P. Note R=(300030003)=3I3R = \begin{pmatrix}3&0&0\\0&3&0\\0&0&3\end{pmatrix} = 3I_3, where I3I_3 is the 3×33\times3 identity matrix. So PR=P(3I3)=3(PI3)=3P,PR = P(3I_3) = 3(PI_3) = 3P, …

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