So there is an identity we'll need to use to solve this:
cos(x+y) = cosxcosy - sinxsiny
replace the numerator with the right hand side of that identity and we get:
(cosxcosy - sinxsiny)/cosxsiny
Separate the numerator into 2 fractions and we get:
cosxcosycosxsiny- sinxsiny/cosxsiny
the cosx's cancel on the left fraction, the siny's cancel on the right fraction and we're left with:
cosy/siny - sinx/cosx
which simplifies to:
coty - tanx
As per the problem
The chemicals in my swimming pool use a ratio of 5 tablets of chlorine for every 14 days.
we have been asked to find
Which ratio shows the number of chlorine tablets needed for 42 days?
Since for each 14 days the number of tablets required is 5
So if you multiply the number of days by some number then, we will have to multiply the number of tablets required by the same number.
So When number of days
Then the number of tablets required for 42 days is 
Answer:
2
Explanation: A plane contains at least three non-collinear points. If two points lie in a plane, then the line containing them lies in the plane. If two planes intersect, then their intersection is a line.