First blank we have 1 /tan u
And 1/ tan u = 1 / (sin u / cos u) = cos u / sin u
So now we have
cos u * sec u * cos u / sin u = cos u * (1 /cos u) * (cos u /sin u)
(The red part goes into the second blank)
And this evaluates to cot u .....which is what we are trying to show !!!!
What is sec though? I know it stands for secant, but I don't know what it is...
Lol geometry is one of my worst subjects.
sec u = 1 /cos u
Sorry....I should have made that a little clearer !!!