Math problem master come in please?

x∈Rf(x²+1)=(x²)²+5x²+2f(x²-1)=?

f(x^2+1)=(x^2+1)^2+3(x^2+1)-2(rearranging the terms)so f(x^2-1)=(x^2-1)^2+3(x^2-1)-2=x^4+x^2-4

if we put x^2+1 as t x^2 = t-1so f(x^2+1) = (x^2)^2 + 5x^2 + 2orf(t) = (t-1)^2 + 5(t-1)+ 1= t^2 -2 t +1 + 5 t - 5 + 2 = t^2 + 3 t -2now put t = x^2 -1 to getf(x^2-1) = (x^2-1)^2 + 3(x^2-1) - 2= x^4 - 2x^2 + 1 + 3x^2 - 3 -2= x^4 +x^2 - 4

x^4 + x² - 4