Mark M. answered 11/03/23
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
1 / (x2 - 8x + 25) = 1 / [(x2 - 8x + 16) + 9] = 1 / [(x - 4)2 + 9]
So, we have 50∫ (1 / [(x-4)2 + 9])dx = (50/9) ∫ (1 / [((x-4)/3)2 + 1])dx
Let u = (x-4)/3. Then du = (1/3)dx. So, dx = 3du.
We then have (50/3) ∫ [1 / (1 + u2)]du = (50/3)Arctanu + C = (50/3)Arctan [(x-4)/3] + C