Answer:
15 cm
Step-by-step explanation:
The altitude is one leg of the right triangle formed by the altitude, half the base, and the triangle side. The Pythagorean theorem applies, so you have ...
... (17 cm)² = (altitude)² + (16 cm/2)²
... altitude = √(17² -8²) cm = √225 cm
... altitude = 15 cm
