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2019 WAEC Further Mathematics Theory Using determinants, solve the following equations simultaneously. 5x — 6y + 4z = 15 7x...

Further Mathematics
WAEC 2019

Using determinants, solve the following equations simultaneously.

5x — 6y + 4z = 15

7x + 4y — 3z = 19

2x + y + 6z = 46 
 

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Explanation

To find the determinant of \(\begin{pmatrix} 5 & -6 & 4\\ 7 & 4 & -3\\ 2 & 1 & 6 \end{pmatrix}\) which is  5(24 + 3) + 6(4 + 6) + 4(7 - 8) = 135 + 288 - 4 = 419.

Then, substitude the column of the coefficient of x by the right - hand side of the equations and find the determinant of \(\begin{pmatrix} 5 & -6 & 4\\ 7 & 4  & -3\\ 46 & 1 & 6 \end{pmatrix}\)  = 15(24 + 3) + 6(114 + 138) + 4(19 - 184) = 405 + 1512 - 660 = 1257. 


Similarly, to find the coefficient of y, find the determinant of \(\begin{pmatrix} 5 & 15 & 4\\ 7 & 19 & -3\\ 2 & 46 & 6 \end{pmatrix}\) 

= 5(114 + 138) - 13(42 + 6) - 4(322 - 38) = 1260 - 720 + 1136 = 1676. 

Finally, for the coefficient of z find the determinant of \(\begin{pmatrix} 5 & -6 & 15\\ 7 & 19 & -3\\ 2 & 46 & 6 \end{pmatrix}\)   

= 5(184 - 19) + 6(322 - 38) + 15(7 - 8) = 825 + 1704 - 15 = 2514

Therefore, x = \(\frac{1257}{419}\) = 3, y = \(\frac{1676}{419}\) = 4 

and z = \(\frac{2514}{419}\) = 6


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Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts