(Solved): valuate the integral: x2x2+6421dx (A) Which trig substitution is correct for this integral ...

valuate the integral: $$?\frac{21}{x^2\sqrt{x^2+64}}dx$$ (A) Which trig substitution is correct for this integral? $$\begin{array}{l}x=64\sec (?)\\ x=21\sec (?)\\ x=8\tan (?)\\ x=8\sin (?)\\ x=64\sin (?)\\ x=64\tan (?)\end{array}$$ (B) Which integral do you obtain after substituting for $$x$$ and simplifying? Note: to enter $$?$$. typoe the word theta $$d?$$ (C) What is the value of the shonvalinwnunid terms of $$?$$ ? + c