Trig Substitution

Question 1

what sub. should be used for
√(a^2 - x^2)

Answer 1

x = asinθ
dx = acosθdθ
√(a^2 - x^2) = acosθ

Question 2

what sub. should be used for
√(a^2 + x^2)

Answer 2

x = atanθ
dx = asec²θdθ
√(a^2 + x^2) = asecθ

Question 3

what sub. should be used for
√(x^2 - a^2)

Answer 3

x = asecθ
dx = asecθtanθdθ
√(x^2 - a^2) = atanθ