if a_1 , a_2 , a_3 , a_4 are the coefficient
of any four four consecutive
terms in the expansion of (1+x)^n
then (a_1 /(a_2 +a_1 ))+(a_3 /(a_3 +a_4 )) is equal to...
just found this on the web
I thought it might help in some cases where
quartics appear i.e. Sir Aifour′s geometric
questions. sometimes we know the nature of
the roots, but how to use this information?
ax^4 +bx^3 +cx^2 +dx+e=0
1. divide by a
2. x=z−(b/(4a))
this leads to the reduced
z^4 +pz^2 +qz+r=0
now we find the nature of the roots:
T_1 =16p^4 r−4p^3 q^2 −128p^2 r^2 +144pq^2 r−27q^4 +256r^3
T_2 =p^2 +12r
T_3 =−p^2 +4r
T_1 <0 ⇒ 2 distinct real and 2 conjugated complex roots
T_1 >0∧(p<0∧T_3 <0) ⇒ 4 distinct real roots
T_1 >0∧(p>0∨T_3 >0) ⇒ 2 pairs of conjugated complex roots
T_1 =0∧(p<0∧T_3 <0∧T_2 ≠0) ⇒ 1 real double and 2 real simple roots
T_1 =0∧(T_3 >0∨(p>0∧(T_3 ≠0∨q≠0))) ⇒ 1 real double and 2 conjugated complex roots
T_1 =0∧(T_2 =0∧T_3 ≠0) ⇒ 1 real triple and 1 real simple roots
T_1 =0∧(T_3 =0∧p<0) ⇒ 2 real double roots
T_1 =0∧(T_3 =0∧p>0∧q=0) ⇒ 2 conjugated complex double roots
T_1 =0∧T_2 =0 ⇒ all roots are equal