When you add 2pi to the angle, the amount is still the same. Therefore, you can make -17pi/4 positive by adding 6pi to it.
6pi + (-17pi/4)
= 24pi/4 - 17pi/4
= 7pi/4
a=c because the transitive property states so.
Use the Pythagorean theorem
a^2 + b^2 = c^2
a^2 + 15^2 = 25^2
a^2 + 225 = 625
a^2 = 400
a = 20
Answer: 20 cm
Hope this helps!!
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0.161 (they said explain it so)