ⓐ f(0)=0 ⓑ f(2π)=−1
ⓒ f(−23π)=−1 ⓓ x=−2π,−π,0,π,2π 일 때 f(x)=0
ⓔ (−2π,0),(−π,0), (0,0),(π,0),(2π,0)
ⓕ (0,0) ⓖ (−∞,∞)
ⓗ [−1,1]
원본 교재 풀이(영어)
ⓐ f(0)=0 ⓑ f(2π)=−1
ⓒ f(−23π)=−1 ⓓ f(x)=0 for x=−2π,−π,0,π,2π
ⓔ (−2π,0),(−π,0), (0,0),(π,0),(2π,0)
ⓕ (0,0) ⓖ (−∞,∞)
ⓗ [−1,1]