# A-level maths; first principles

"You may assume the formula for cos(A ± B) and as h 0, sin (h)/h 1 and cos(h)-1 /h 0"

I was just wondering, will the question always provide this rule, or should it be learnt? (This is for edexcel)
Original post by poppjngcandy
"You may assume the formula for cos(A ± B) and as h 0, sin (h)/h 1 and cos(h)-1 /h 0"
I was just wondering, will the question always provide this rule, or should it be learnt? (This is for edexcel)

The first rule should be covered in Trig, and the last two in the introductory part of Calculus concerning limits. I memorized them for my A-levels (that's a while ago). If your teacher has shown the proof (i.e., derived it in class or if it's the assigned readings), you should memorize them. More useful is to get hold of the exam syllabus. So you know what you are supposed to know for the particular exams.
Original post by poppjngcandy
"You may assume the formula for cos(A ± B) and as h 0, sin (h)/h 1 and cos(h)-1 /h 0"
I was just wondering, will the question always provide this rule, or should it be learnt? (This is for edexcel)

all it is is that when you get to the stage where it is sin(h)/h you use small angle approximations, so sin(h) --> h where h/h=1 this is the same for cos(h)-1/h, so cos(h) --> 1 - ((h^2)/2), and when you simplify it is 0.