Example 1easy
- A)0
- B)1
- C)44
- D)89/2
Step-by-step solution
- The first sum is S1 = sin²1° + sin²2° + ... + sin²89°. We can pair terms using sin²A + sin²(90°-A) = sin²A + cos²A = 1.
- S1 = (sin²1° + sin²89°) + (sin²2° + sin²88°) + ... + (sin²44° + sin²46°) + sin²45°. This gives 44 pairs, each summing to 1, plus sin²45°.
- So, S1 = 44 × 1 + (1/√2)² = 44 + 1/2 = 89/2.
- Similarly, the second sum is S2 = cos²1° + cos²2° + ... + cos²89°. Using cos²A + cos²(90°-A) = cos²A + sin²A = 1, S2 = 89/2.
- Therefore, the expression is S1 - S2 = 89/2 - 89/2 = 0.
Answer: 0