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Find the matrix T if ST = I where S = \(\begin{pmatrix} -1 & 1...

Mathematics
JAMB 1999

Find the matrix T if ST = I where S = \(\begin{pmatrix} -1 & 1 \\ 1 & -2 \end{pmatrix}\)

  • A. \(\begin{pmatrix} -2 & -1 \\ -1 & -1 \end{pmatrix}\)
  • B. \(\begin{pmatrix} -2 & -1 \\ -1 & 1 \end{pmatrix}\)
  • C. \(\begin{pmatrix} -1 & -1 \\ 0 & -1 \end{pmatrix}\)
  • D. \(\begin{pmatrix} -1 & 1 \\ 0 & 1 \end{pmatrix}\)
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Correct Answer: Option A
Explanation

S = \(\begin{pmatrix} -1 & 1 \\ 1 & -2 \end{pmatrix}\)
and ST = I  (Identity matrix).

This means  T  is the inverse of S 

Find the determinant of S  
\( \det(S)\) = (-1)(-2) - (1)(1) = 2 - 1 = 1

T = \(\frac{1}{\det(S)} \begin{pmatrix} -2 & -1 \\ -1 & -1 \end{pmatrix}\)
Since det = 1,  
T = \(\begin{pmatrix} -2 & -1 \\ -1 & -1 \end{pmatrix}\)
T = \(\begin{pmatrix} -2 & -1 \\ -1 & -1 \end{pmatrix}\)


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WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076
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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
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WAEC offline past questions - with all answers and explanations in one app - Download for free
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WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC and NECO CBT App for Mobile Devices - Candidates, Schools, Centres, Resellers - 100% Offline -Download Now
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 127076