If f(x) is a polynomial of degree 4 with rational coefficients and touches x-axis at (2,0), then for the equation f(x) = 0,
sum of roots is 42
sum of roots is 0
product of roots is -4
product of roots is 4
It is given that f(x) touches x-axis at (2,0). So, two roots are 2,2.
Sine coefficients are rational, other roots must be −2,−2.