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Mohan and Sohan solve an equation. In solving Mohan commits a mistake in constant term and finds the roots 8 and 2. Sohan commits a mistake in the coefficient of x. The correct roots are
  • a)
    9, 1
  • b)
    -9, 1
  • c)
    9, -1
  • d)
    -9, -1
Correct answer is option 'A'. Can you explain this answer?
Verified Answer
Mohan and Sohan solve an equation. In solving Mohan commits a mistake...
Correct sum = 8 + 2 = 10 from Mohan
Correct product = -9 x -1 = 9 from Sohan
∴ x2 – (10)x + 9 = 0
⇒ x2 – 10x + 9 = 0
⇒ x2 – 9x – x + 9
⇒ x(x – 9) – 1(x – 9) = 0
⇒ (x - 9) (x -1) = 0 .
⇒ Correct roots are 9 and 1.
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Most Upvoted Answer
Mohan and Sohan solve an equation. In solving Mohan commits a mistake...
Given information:
- Mohan made a mistake in the constant term and got roots 8 and 2.
- Sohan made a mistake in the coefficient of x.

Let's denote the correct roots as a and b.

Mistake in constant term
If Mohan made a mistake in the constant term, it means he changed the constant term from c to k.

The equation with roots 8 and 2 can be written as:
(x - 8)(x - 2) = 0

Expanding this equation, we get:
x^2 - 10x + 16 = 0

But Mohan made a mistake in the constant term, so he wrote the equation as:
x^2 - 10x + k = 0

Let's find the value of k.

We know that the sum of roots of a quadratic equation is -b/a.
So, a+b = 10/1 = 10

We also know that the product of roots of a quadratic equation is c/a.
So, ab = 16/1 = 16

Using these two equations, we can find the value of k as follows:
(x-a)(x-b) = x^2 - (a+b)x + ab = x^2 - 10x + 16
So, k = ab = 16

Therefore, the equation with the correct constant term is:
x^2 - 10x + 16 = 0

Mistake in coefficient of x
If Sohan made a mistake in the coefficient of x, it means he changed the coefficient from 1 to -1.

The equation with correct roots a and b can be written as:
(x - a)(x - b) = 0

If we expand this equation, we get:
x^2 - (a+b)x + ab = 0

But Sohan made a mistake in the coefficient of x, so he wrote the equation as:
-x^2 + (a+b)x - ab = 0

Let's find the roots of this equation using the quadratic formula:
x = (-b ± sqrt(b^2 - 4ac)) / 2a
where a = -1, b = (a+b), and c = -ab

Substituting the values of a, b, and c, we get:
x = (-(a+b) ± sqrt((a+b)^2 + 4ab)) / 2(-1)

Simplifying this expression, we get:
x = (-(a+b) ± sqrt((a-b)^2)) / 2

Since the discriminant is zero, the roots are real and equal.
So, we have:
-(a+b) ± (a-b) = 0

Solving these two equations, we get:
a = 9 and b = 1

Therefore, the correct roots are 9 and 1, which is option A.
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Mohan and Sohan solve an equation. In solving Mohan commits a mistake in constant term and finds the roots 8 and 2. Sohan commits a mistake in the coefficient of x. The correct roots area)9, 1b)-9, 1c)9, -1d)-9, -1Correct answer is option 'A'. Can you explain this answer?
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