Question

Triangle DEF has side lengths e=9 and f=13. If the measure of angle D is 41°, what is the length of side d?

• 13.5
• 5.1
• 6.9
• 8.6

Answer 1

8.6

Explanation:

Use the law of cosines

`d^(2) = e^(2) + f^(2) -2ef cos D`

`d^(2) = 9^(2) + 13^(2) - 2(9)(13) cos 41\\ = 81 + 169 - 176.602\\ = 73.3979\\d = √(73.3979) = 8.6`