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Q.

Solve the following pairs of equations.


2 x + 3 y =2 4 x 9 y =1


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a

The solution of the given system of equation is x=4 and y=9 .

b

The solution of the given system of equation is x=4 and y=9 .

c

The solution of the given system of equation is x=4 and y=9 .

d

The solution of the given system of equation is x=4 and y=9 . 

answer is A.

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Detailed Solution

Given equations are,
2 x + 3 y =2.............(1) 4 x 9 y =1.............(2)
We know that if the two linear equations are a 1 x+ b 1 y+ c 1 =0 a 2 x+ b 2 y+ c 2 =0 then the cross-multiplication formula is x b 1 c 2 b 2 c 1 = y c 1 a 2 c 2 a 1 = 1   b 2 a 1 b 1 a 2 .
Let us assume 1 x =m, 1 y =n So, equation (1) and (2) becomes
2m+3n=2 ......(3)
4m9n=1 ......(4)
Convert equation (3) and (4) in linear standard form.
am+bn+c=0 2m+3n=2 2m+3n2=0 .......(5)
4m9n=1 4m9n+1=0 ......(6)
Compare equation (5) 2 m+3n2=0 with standard linear equation. We get, a 1 =2,  b 1 =3 and  c 1 =2.
Now, compare equation (6), 4 m9n+1=0 with standard linear equation. We get, a 2 =4,  b 2 =9 and  c 2 =1.
Using the formula of cross multiplication.
m b 1 c 2 b 2 c 1 = n c 1 a 2 c 2 a 1 = 1   b 2 a 1 b 1 a 2 Put the value of a 1 =2, b 1 =3, c 1 =2, a 2 =4, b 2 =9 and c 2 =1 in above formula. m 3(1)(9)(2) = n 2(4)1(2) = 1 (9)(2)3(4) m 318 = n 82 = 1 1812 m 15 = n 10 = 1 30 Taking first and third term
m 15 = 1 30 m= 15 30 m= 1 2 Now, taking second and third term.
n 10 = 1 30 n= 1 3 since, 1 x =m 1 x = 1 2 x =2 x= 2 2 x = 4
And 1 y =n 1 y = 1 3 y =3 y= 3 2 y = 9
Therefore, the solution of the given equations is x=4 and y=9 .
The correct option is (1).
 
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