I'm also attaching a screenshot of the previous calculation.
https://www.wolframalpha.com/input?i2d=true&i=Power%5B2%2C%5C%2840%29%5C%2840%29Divide%5BDivide%5B%5C%2840%293%5C%2840%29n%2B2%5C%2841%29%2B1%5C%2841%29%2C2%5D%2C2%5D-Divide%5BDivide%5B%5C%2840%293Divide%5B%5C%2840%29n%2B3%5C%2841%29%2C2%5D%2B1%5C%2841%29%2C2%5D%2C2%5D%5C%2841%29-%5C%2840%29n%2B1%5C%2841%29%5C%2840%29Divide%5B3%2C8%5D%5C%2841%29%5C%2841%29%2B%5C%2840%29%5C%2840%29Divide%5BDivide%5B%5C%2840%293%5C%2840%29n%2B1%5C%2841%29%2B1%5C%2841%29%2C2%5D%2C2%5D-Divide%5BDivide%5B%5C%2840%293Divide%5B%5C%2840%29n%2B2%5C%2841%29%2C2%5D%2B1%5C%2841%29%2C2%5D%2C2%5D%5C%2841%29-%5C%2840%29n%5C%2841%29%5C%2840%29Divide%5B3%2C8%5D%5C%2841%29%5C%2841%29%2B%5C%2840%29%5C%2840%29%5C%2840%29-3%5C%2840%29-n%5C%2841%29%2B1%5C%2841%29-%5C%2840%293n%2B1%5C%2841%29%5C%2841%29%5C%2841%29%2B%5C%2840%29%5C%2840%29Divide%5B%5C%2840%29Power%5B2%2Cn%5D*3%5C%2840%29Power%5B2%2C%5C%2840%29n-1%5C%2841%29%5D%5C%2841%29%2C4%5D%5C%2841%29-%5C%2840%29Power%5B2%2C%5C%2840%29n-1%5C%2841%29%5D*3%5C%2840%29Power%5B2%2C%5C%2840%29n-2%5C%2841%29%5D%5C%2841%29%5C%2841%29%5C%2841%29%5D%3D1
