x<=2,y=2^(2x+2) − 2^(x+2) https://www.wolframalpha.com/input?i=x%3C%3D2%2Cy%3D2%5E%282x%2B2%29+%E2%88%92+2%5E%28x%2B2%29+&lang=ja
x<=2,y=2^(2x+2) − 2^(x+2)
https://www.wolframalpha.com/input?i=x%3C%3D2%2Cy%3D2%5E%282x%2B2%29+%E2%88%92+2%5E%28x%2B2%29+&lang=ja