I need about 2 of these but pls explain so I can learn and try on my own pls

These problems are based on the Pythagorean Theorem. The Pythagorean Theorem is a^2 + b^2 = c^2. If the two sides are equal, the triangle is a right triangle. If c^2 is less, the triangle is acute. If c^2 is more, the triangle is obtuse.

Obtuse: c^2 > a^2 + b^2

Acute: c^2 < a^2 + b^2

Right: c^2 = a^2 + b^2

#7 --- Obtuse

21^2 ___ 8^2 + 15^2

441 ___ 64 + 225

441 > 289

#8 --- Right

20^2 ___ 12^2 + 16^2

400 ___ 144 + 256

400 = 400

#9 --- Acute

6^2 ___ 4^2 + 5^2

36 ___ 16 + 25

36 < 41

Hope this helps!