1 answer
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(x+2)^4 = x^4+4x^3*2 + 6x^2*2^2 + 4x*2^3 + 2^4 = x^4+8x^3+24x^2+32x+16
Now multiply that by 1 + 1/x^2 and you get
... + 24x^2 + ... + x^2 = 25x^2