In the 1st video of integration by parts in question [xcos inverse 1] /[under root(1-x*x)] after solving, how sint become [under root(1-x*x)]

We substituted cos^-1x = t

=> cos t = x

=> cos²t = x²                [By squaring both sides]

=> 1 - sin²t = x²           [Using identity sin²t + cos²t = 1]

=> 1 - x² = sin²t

=> sint = root (1 - x²)