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
The answer to this would be C
Sure.
The common difference is 1/3
d = 8/15 - 1/5 = 8/15 - 3/15 = 5/15 = 1/3
d = 13/15 - 8/15 = 5/15 = 1/3
So the seventh term is
S_n = S_1 + (n-1)d
S_7 = (1/5) + 6(1/3) = 11/5
The sum is the average of the first and last times the number of elements
(1/2)(1/5 + 11/5)(7) = 7(6/5) = 42/5 = 8.4
Answer: 42/5
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