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If  (x1,y1)(x_1, y_1)(x1​,y1​)​ is the solution of the pair of equations: x10+y5−1=0\frac{x}{10} + \frac{y}{5} - 1 = 010x​+5y​−1=0​&nbs
Question

If  (x1,y1)(x_1, y_1)​ is the solution of the pair of equations: x10+y51=0\frac{x}{10} + \frac{y}{5} - 1 = 0​ andx8+y6=15 \quad \frac{x}{8} + \frac{y}{6} = 15 \\ 
and y1=λx1+5, y_1 = \lambda x_1 + 5,​ then the value of λ \lambda​ is:

A.

2

B.

12\frac{1}{2} ​​

C.

12 -\frac{1}{2} ​​

D.

- 2

Correct option is C

Given:
x10+y51=0(1)x8+y6=15(2)y1=λx1+5\frac{x}{10} + \frac{y}{5} - 1 = 0 \quad \text{(1)} \\\frac{x}{8} + \frac{y}{6} = 15 \quad \text{(2)} \\y_1 = \lambda x_1 + 5 \\​​
Solution:
From (1):x10+y5=1 \quad \frac{x}{10} + \frac{y}{5} = 1 \\​​
=>x10+2y10=1=>x+2y10=1=>x+2y=10.....A\Rightarrow \frac{x}{10} + \frac{2y}{10} = 1 \\\Rightarrow \frac{x + 2y}{10} = 1 \\\Rightarrow x + 2y = 10 {.....A} \\​​
From (2):
x8+y6=15=>3x24+4y24=15=>3x+4y24=15=>3x+4y=360........B\frac{x}{8} + \frac{y}{6} = 15 \\\Rightarrow \frac{3x}{24} + \frac{4y}{24} = 15 \\\Rightarrow \frac{3x + 4y}{24} = 15 \\\Rightarrow 3x + 4y = 360 {........B} \\​​
From (A): x=102y \quad x = 10 - 2y \\​​
Substitute in (B):
3(102y)+4y=360306y+4y=3602y=330=>y=165x=102(165)=10+330=3403(10 - 2y) + 4y = 360 \\30 - 6y + 4y = 360 \\-2y = 330 \Rightarrow y = -165 \\x = 10 - 2(-165) = 10 + 330 = 340 \\​​
Now use: y1=λx1+5\quad y_1 = \lambda x_1 + 5 \\​​
165=λ(340)+5λ(340)=170λ=170340=12-165 = \lambda(340) + 5 \\\lambda(340) = -170 \\\lambda = \frac{-170}{340} = -\frac{1}{2} \\​​
Correct answer is (c)

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