4. Evaluate the geometric series given a1 = 4, r = -2 and n = 12
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Answer:
17
Step-by-step explanation:
Using the law of cosines in ΔABC
b² = a² + c² - (2ac cosB) ← substitute in values
= 25² + 28² - (2 × 25 × 28 × cos36.9°)
= 625 + 784 - 1400 cos36.9°
= 1409 - 1400 cos36.9° ( Take the square root of both sides )
b = ≈ 17 ( nearest whole number )