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Mathematics

Assertion (A): The value of sin2 30° - 2 cos3 60° + 2 tan4 45° is 2.

Reason (R): sin 30° = 12\dfrac{1}{2}, cos 60° = 12\dfrac{1}{2}, and tan 45° = 1

  1. A is true, but R is false.

  2. A is false, but R is true.

  3. Both A and R are true, and R is the correct reason for A.

  4. Both A and R are true, and R is the incorrect reason for A.

Trigonometrical Ratios

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Answer

We know that,

sin 30° = 12\dfrac{1}{2}, cos 60° = 12\dfrac{1}{2}, and tan 45° = 1.

So, reason (R) is true.

sin230°2 cos360°+2 tan445°=(12)22×(12)3+2×14=142×18+2=1414+2=2.\text{sin}^2 30° - \text{2 cos}^3 60° + \text{2 tan}^4 45° = \Big(\dfrac{1}{2}\Big)^2 - 2 \times \Big(\dfrac{1}{2}\Big)^3 + 2 \times 1^4\\[1em] = \dfrac{1}{4} - 2 \times \dfrac{1}{8} + 2\\[1em] = \dfrac{1}{4} - \dfrac{1}{4} + 2\\[1em] = 2.

So, assertion (A) is true.

∴ Both A and R are true, and R is the correct reason for A.

Hence, option 3 is the correct option.

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