Please help me with the following question. Thank you so much!

Shown below are my limits of integration before converting my x-values to the favalues 4x S I cos 0 1 x / cosol x do Ih X = ? s cos a do so dx = ? X = 0 -> A=0 X = 4 -0 = 2 A If I chose the simplest looking substitution with no radicals , what simple substitution did I most likely use for X based on my triangle! What would the original definite integral have been in terms of x ? " For the next step , how can I rewrite cos O so that I can integrate it