Which is a not a triangle ?

Answer:
answer: d
Step-by-step explanation:
idek how to explain.
Answer:
The answer is C.
Step-by-step explanation:
A: 6²+8²=10²
B: 8²+15²=17
C: 11²+24²≠25
D: 20²+21²=29²
So, the answer is C.
Note:
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