What is value of f(x+3) , if f(x+1)=2x^2 -11x+3

we have 
x+ 3 = (x+1) + 2

as f(x+1) = 2x^2 -11x+3

so f(x+3) = 2(x+2)^2 - 11(x+ 2) + 3 = 2(x^2 + 4x + 4) - 11(x+2) + 3 = 2x^2 -3x - 11
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(rationale

f(x+1) = 2x^2 - 11x + 3

let x + 1 = y

so f(y) = 2(y-1) ^2 - 11y + 3

so f(y+2) = 2(y+1)^2 - 11(y+1) + 3

hence f(x+3) = 2(x+2)^2 - 11(x+2) + 3)