I have a diagram showing triangle ABC.
Line AB is 1.8 cm, line AC is 2.7 cm, and line BC is 3.6 cm.
I have to work out the size of angle A and then the area of the triangle.
Can anyone help? Please show workings! :)
Triangle maths questions?
2016-06-14 4:56 pm
回答 (2)
2016-06-14 5:17 pm
✔ 最佳答案
cosA = (AB² + AC² - BC²) / (2 × AB × AC) ...... (cosine law)cosA = (1.8² + 2.7² - 3.6²) / (2 × 1.8 × 2.7)
A = 104.5°
Area of ΔABC
= (1/2) × AB × AC × sinA
= (1/2) × 1.8 × 2.7 × sin104.5° cm²
= 2.35 cm²
OR:
s = (1.8 + 2.7 + 3.6)/2 cn
s = 4.05 cm
Area of ΔABC
= √[s(s - AB)(s - AC)(s - BC)]
= √[4.05 × (4.05 - 1.8) × (4.05 - 2.7) × (4.05 - 3.6)] cm²
= 2.35 cm²
2016-06-14 5:02 pm
Use the Law of Cosines
∠A = arccos( (2.7²+1.8²-3.6²) / (2·2.7·1.8))
∠A = arccos( (2.7²+1.8²-3.6²) / (2·2.7·1.8))
收錄日期: 2021-04-18 15:04:56
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20160614085659AAyjskf