Question

whats cos(arctan 4) without using a caculator

Answer 1

let arctan4=x
then tanx=4
draw your right triangle that goes nicely with this
meaning opposite side is 4 and adjacent is 1
hence the hyp should be root(17)
now take cosine of that angle (which is the same as saying cos(artan4)
cos(arctan4)=1/root(17)=root(17)/17
check it by calculator and see if that's true

Answer 2

the diagram should be like this

Answer 3

Thank you very much! :)

Answer 4

welcome!