What is the trigonometric form of 9 e^( ( pi)/2 i ) ?

Use the fact that ${e}^{a \cdot i} = \cos a + i \cdot \sin a$ hence
$9 \cdot {e}^{\frac{\pi}{2} \cdot i} = 9 \cdot \left(\cos \left(\frac{\pi}{2}\right) + i \cdot \sin \left(\frac{\pi}{2}\right)\right)$