Cos( A + B ) = cosAcosB - sinAsinB ;
cos( A + B ) / ( cosAsinB ) = ( cosAcosB - sinAsinB ) / ( cosAsinB ) = ( cosAcosB ) / ( cosAsinB ) - ( sinAsinB ) / ( cosAsinB ) = cosB / sinB - sinA / cosA = cotB - tanA ;
Answer:
Explanation:
The missing equation is:

You are given:
- Ta = the temperature surrounding the object = 73ºF
- T₀ = the initial temperature of the object = 204ºF
- t = 2.5 min
- T after 2.5 min = 180ºF
Question 1: Find the the value of k.
Substitute the data into the equation and solve for k:

Question 2: Find the Fahrenheit temperature of the cup of water, to the nearest degree, after 4 minutes.
Subsititute into the formula and compute:

1/3+2/9=1/6x-4/6
3/9+2/9=1/6x-4/6
5/9=1/9x-4/6
5=x-6
x=11