1.  x 3 We know this integral: But what about this integral:
Playing around with the Substitution method would give us the answer but let’s try a different approach:
Consider that 9 + x2 is the sum of two squares. Then if we made 9 and x two sides of a right triangle…
…and we can safely say given this info that…

2. We know this integral: x
But what about this integral:  3

3. But what about this integral:3 x 

4. But what about this integral:x  3

5. Trigonometric Substitutions

6. #36 5 t 
Half-Angle Formula

7. #36 5 t 
Double-Angle Formula