Answer:
A
Step-by-step explanation:
Given 2 sides and the included angle use the Cosine rule to solve for x
x² = 1.6² + 1.1² - (2 × 1.6 × 1.1 × cos78° )
= 2.56 + 1.21 - ( 3.52 × cos78° )
= 3.77 - 0.7318
= 3.0382
Take the square root of both sides
x = = 1.7 → A