If x2−3x+2 is a factor of  x4−ax2+b=0 then the equation whose roots are a and b is

x4−ax2+b=x2−3x+2p(x)  =(x−1)(x−2)p(x)where p(x) is a polynomial of degree 2∴1−a+b=0   and  16−4a+b=0⇒a=5,b=4Thus, equation whose roots are a and b isx2−9x+20=0