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Question -

Solve the following pair of linear equations by the substitution and cross-multiplication methods:



Answer -

8x + 5y = 9
3x + 2y = 4

Solution:
8x + 5y = 9 …………………..(1)
3x + 2y = 4 ……………….….(2)
From equation (2) we get
x = (4 – 2y )/ 3  ……………………. (3)
Using this value in equation 1, we get
8(4-2y)/3 + 5y = 9
32 – 16y +15y = 27
-y = -5
y = 5 ……………………………….(4)
Using this value in equation (2), we get
3x + 10 = 4
x = -2
Thus, x = -2 and y = 5.
Now, Using Cross Multiplication method:
8x +5y – 9 = 0
3x + 2y – 4 = 0
x/(-20+18) = y/(-27 + 32 ) = 1/(16-15)
-x/2 = y/5 =1/1
∴ x = -2 and y =5.

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