Question

Solve the following pair of linear equations by the substitution method.

(i) x + y = 14
x – y = 4

(ii) 3x – y = 3
9x – 3y = 9​

Answer 1

⠀⠀ıllıllı uoᴉʇnloS ıllıllı

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(i) Given:

x + y = 14 and x - y = 4 are the two equations.

From 1st equation, we get:

• x = 14 - y

Now, put the value of x in second equation to get,

(14 - y) - y = 4

➠ 14 - 2y = 4

➠ 2y = 10

➠ Or y = 5

By the value of y, we can now find the exact value of x;

∵ x = 14 - y

∴ x = 14 - 5

Or x = 9

• Hence, x = 9 and y = 5.

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(ii) Given:

3x - y = 3 and 9x - 3y = 9 are the two equations.

From 1st equation, we get,

• x = (3 + y)/3

Now, substitute the value of x in the given second equation to get,

9(3 + y)/3 - 3y = 9

➠ 3(3 + y) - 3y = 9

➠ 9 + 3y - 3y = 9

➠ 9 = 9

• Therefore, y has infinite values and since, x = (3 + y)/3, so x also has infinite values.

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Answer 2

Answer:

x=14-y

14-y-y=4

-2y=-10

y=10 ANS.

x=4 ANS.

ii) 3x=3+y

x=3+y/3

9 ×3+y/3 - 3y=9

9+3y-3y=9

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