Answer:
The value of cos Ф is ± 
Step-by-step explanation:
There are important rules for sin Ф and cos Ф
∵ sin Ф = 
∴ sin²Ф = 
∴ sin²Ф = 
→ By using the third rule above
∵ cos²Ф = 1 - sin²Ф
∴ cos²Ф = 1 - 
∴ cos²Ф = 
→ Take square root for both sides
∴ cos Ф = ± 
∴ The value of cos Ф is ± 
Fractions can be converted to decimals and vice versa.
<em>The decimal equivalent of the fraction of months with 31 days is 0.583</em>
Given:
<em />
<em> --- months in a year</em>
<em />
<em> --- months with 31 days</em>
<em />
The fraction (n) of months with 31 days is:

So, we have:

The decimal equivalent is:

Hence, (c) is correct.
Read more about fractions and decimals at:
brainly.com/question/548650
A couple is 2. Hope this helps.
81 cent.........................................................
Given 2 angle : 45 and 90 (right angle)
==> 180-45-90 = 45