 ## Book: RD Sharma - Mathematics (Volume 1)

### Chapter: 4. Inverse Trigonometric Functions

#### Subject: Maths - Class 12th

##### Q. No. 25 of MCQ

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25
##### Choose the correct answerIf , then the value of x is

We are given that, …(i)

We need to find the value of x.

Using the property of inverse trigonometry, Replace A by and B by . Putting this value in equation (i),  Taking tangent on both sides, Using the property of inverse trigonometry,

tan(tan-1 A) = A Cross-multiplying, we get Simplifying the equation in order to find the value of x, Let us cancel the denominator from both sides of the equation.

x(x + 1) + (x – 1)(x – 1) = -7[x(x – 1) – (x + 1)(x – 1)]

x2 + x + (x – 1)2 = -7[x2 – x – (x + 1)(x – 1)]

Using the algebraic identity,

(a – b) = a2 + b2 – 2ab

And, (a + b)(a – b) = a2 – b2

x2 + x + x2 + 1 – 2x = -7[x2 – x – (x2 – 1)]

2x2 – x + 1 = -7[x2 – x – x2 + 1]

2x2 – x + 1 = -7[1 – x]

2x2 – x + 1 = -7 + 7x

2x2 – x – 7x + 1 + 7 = 0

2x2 – 8x + 8 = 0

2(x2 – 4x + 4) = 0

x2 – 4x + 4 = 0

We need to solve the quadratic equation to find the value of x.

x2 – 2x – 2x + 4 = 0

x(x – 2) – 2(x – 2) = 0

(x – 2)(x – 2) = 0

x = 2 or x = 2

Hence, x = 2.

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