What is the fourth term (k = 3) for (x + y)^11?
1 answer:
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Answer:
The value of cos Ф is ±
Step-by-step explanation:
There are important rules for sin Ф and cos Ф
- sin²Ф + cos²Ф = 1
- sin²Ф = 1 - cos²Ф
- cos²Ф = 1 - sin²Ф
∵ sin Ф =
∴ sin²Ф =
∴ sin²Ф =
→ By using the third rule above
∵ cos²Ф = 1 - sin²Ф
∴ cos²Ф = 1 -
∴ cos²Ф =
→ Take square root for both sides
∴ cos Ф = ±
∴ The value of cos Ф is ±