I have to integrate using parts, but there is one step I don't understand, please can someone explain it?
When integrating sqrt(a^2-z^2) you get:
zsqrt(a^2-z^2) - integral(-z^2/(sqrt(a^2-z^2)))
which can then be split into:
zsqrt(a^2-z^2) - integral(a^2-z^2/(sqrt(a^2-z^2))) - integral(a^2/(sqrt(a^2-z^2)))
Now the next step is written:
integral 2sqrt(a^2-z^2)=zsqrt(a^2-z^2) - integral(a/(sqrt(1-(z/a)^2)))
I don't see how this was generated, as it doesn't seem like everything has been multiplied by 2 as it should have been done?