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Statement-1: The numbers sin18^(@)and-si...

Statement-1: The numbers `sin18^(@)and-sin54^(@)` are the roots of the quadratic equation with integer coefficients.
Statement-2: If `x=18^(@),cos3x=sin2x and If y=-54^(@), sin2y =cos 3y.`

A

Both Statement I and Statement II are individually true and R is the correct explanation of Statement I.

B

Both Statement I and Statement II are individually true but Statement II is not the correct explanaton of Statement I.

C

Statement I is true but Statement II is false.

D

Statement I is false but Statement II is true.

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to verify both statements and show that the numbers \( \sin 18^\circ \) and \( -\sin 54^\circ \) are indeed the roots of a quadratic equation with integer coefficients. We will also analyze the relationships given in Statement 2. ### Step 1: Verify Statement 1 We need to show that \( \sin 18^\circ \) and \( -\sin 54^\circ \) are roots of a quadratic equation with integer coefficients. 1. **Using the identity**: We know that \( \sin 54^\circ = \cos 36^\circ \) and \( \sin 18^\circ = \cos 72^\circ \). - We can use the fact that \( \sin 54^\circ = \sin(90^\circ - 36^\circ) = \cos 36^\circ \). 2. **Expressing \( -\sin 54^\circ \)**: \[ -\sin 54^\circ = -\cos 36^\circ \] 3. **Finding a relationship**: - We know that \( \sin 18^\circ = \frac{\sqrt{5}-1}{4} \) and \( \sin 54^\circ = \frac{\sqrt{5}+1}{4} \). - Thus, \( -\sin 54^\circ = -\frac{\sqrt{5}+1}{4} \). ### Step 2: Form the Quadratic Equation We can form a quadratic equation with roots \( \sin 18^\circ \) and \( -\sin 54^\circ \). 1. **Sum of roots**: \[ \text{Sum} = \sin 18^\circ + (-\sin 54^\circ) = \frac{\sqrt{5}-1}{4} - \frac{\sqrt{5}+1}{4} = \frac{-2}{4} = -\frac{1}{2} \] 2. **Product of roots**: \[ \text{Product} = \sin 18^\circ \cdot (-\sin 54^\circ) = \left(\frac{\sqrt{5}-1}{4}\right) \cdot \left(-\frac{\sqrt{5}+1}{4}\right) = -\frac{(\sqrt{5}-1)(\sqrt{5}+1)}{16} = -\frac{5-1}{16} = -\frac{4}{16} = -\frac{1}{4} \] 3. **Quadratic equation**: Using the sum and product of roots, we can write the quadratic equation as: \[ x^2 - \left(-\frac{1}{2}\right)x - \left(-\frac{1}{4}\right) = 0 \] Multiplying through by 4 to eliminate fractions: \[ 4x^2 + 2x + 1 = 0 \] ### Step 3: Verify Statement 2 Now we need to verify the second statement, which involves the equations given. 1. **For \( x = 18^\circ \)**: \[ \cos 3x = \sin 2x \] - Using the identities, we can rewrite: \[ \cos 54^\circ = \sin 36^\circ \] - This holds true since \( \cos 54^\circ = \sin(90^\circ - 54^\circ) = \sin 36^\circ \). 2. **For \( y = -54^\circ \)**: \[ \sin 2y = \cos 3y \] - Rewriting gives: \[ \sin(-108^\circ) = \cos(-162^\circ) \] - This is also true since \( \sin(-\theta) = -\sin(\theta) \) and \( \cos(-\theta) = \cos(\theta) \). ### Conclusion Both statements are true, and we have shown that \( \sin 18^\circ \) and \( -\sin 54^\circ \) are indeed the roots of a quadratic equation with integer coefficients.
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