Number 21 please help me

Answer:
Yes, doubling the numbers also results in a Pythagorean Triple
Step-by-step explanation:
The reason 3, 4, and 5 form a Pythagorean Triple is because they satisfy the Pythagorean Theorem, which is
a² + b² = c²
3² + 4² = 5²
9 + 16 = 25
25 = 25
Doubling the numbers results in...
6² + 8² = 10²
36 + 64 = 100
100 = 100
They both satisfy the equation.
Another way to think of is that if we double something, we multiply every thing by 2, so we can write the equation like this...
2(a² + b² = c²) so you can read it as two times any numbers that make a Pythagorean Triple