Question

7x+3y=15;12y-5x=39 by Cramer rule

Answer 1

12y-5x=39
-5x+12y=39

d = 7  3
     -5  12
= 7 x 12 - (-5) x 3
= 84 + 15
= 99 

dx= 15   3
        39   12
= 15 x 12 - 39 x 3
= 180 - 117
= 63

dy = 7   15
      -5      39
= 7 x 39 - (-5) x 15
= 348

by cramer's rule
x = dx/d
= 63/99
= 7/11

y= dy/d
= 348/99
= 116/33

Answer 2

7x +3y=15 -----1 12y- 5x=39-------2 5x-12y=39-----3 multiply 1 equaton by 4 4( 7x+3y =15) 28x+ 12y=60----4 3+4 28x+12y=60 5x-12y=39 ------------- 33x=99 x=3 put x=3 in eq 1 7x+3y=15 7×3+3×y= 15 21+3y= 15 21- 15=-3y 6= -3y y= -2

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