Question

21. If 31x+ 43y= 117 and 43x+31y =105, then the value of (x-y) is :
(2) -3 (b) 1/3 (c) -1/3 (d) 3.​

Answer 1

Step-by-step explanation:

31x + 43y = 117 -----------(1)

43x + 31y = 105 ------------(2)

on multiply by 43 in eq. 1 and 31 in eq. 2

43(31x + 43y = 117)

1333x + 1849y = 5031 -----(3)

31(43x + 31y = 105)

1333x + 961y = 3255 ------(4)

on subtract eq. 4 by 3

1333x + 1849y = 5031

1333x + 961y = 3255

- - -

888y = 1776

y = 2

put y in eq 1.

31x + 43y = 117

31x + 43×2 = 117

31x + 86 = 117

31x = 117 - 86

31x = 31

x = 1