If we know your Pythagorean Triples we can immediately recognize that the last choice is a right triangle:
8² + 15² = 17²
If you don't know your Pythagorean Triples, it's worth learning the first few off the list because teachers use them in problems all the time. But for now let's just exhaustively check the Pythagorean Theorem for each triangle. We don't have to multiply everything out; we can analyze the common factors. If two have a common factor that the third one doesn't have, there's no way for the Pythagorean Theorem to add up.
Clearly 5²+15² is a multiple of 5 but 18² isn't so that one isn't a right triangle.
6²+12² is a multiple of 6, 16² isn't a multiple of 6, not an RT.
15²-5² is a multiple of 5, 13² isn't, no joy.
8²+15² = 64 + 225 = 289 = 17² -- that's a real right triangle, a valid Pythagorean Triple.
Answer:
x=7 because 25-4=21 and 21 ÷3=7
Equal them to each other and you get that x=7
Answer:

Step-by-step explanation:



Answer:
Yi Xing invented the astronomical clock and introduced some new methods of interpolation in mathematics.
Step-by-step explanation:
Yi Xing was both an astronomer and a mathematician during the era. He invented the astronomical clock which was more accurate than the initial water and Sun's clock in use.
Furthermore, Yi Xing also discovered some new methods of interpolation in mathematics of which the meaning and interpretation became controversial. Interpolation is a method majorly in mathematics that can be used to estimate a value of a function from its discrete values. It involves first order differences and second order differences.
Also, Yi Xing was able to design a calendar in A.D. 727.