(x^2-3x+1) (x^2+3x+2)( x^2-9x+20)= -30求X

數(shù)學(xué)人氣：348 ℃時(shí)間：2020-05-08 07:13:41

優(yōu)質(zhì)解答

(x-3x+1)(x+3x+2)( x-9x+20) =(x-3x+1)(x+1)(x+2)(x-4)(x-5) =(x-3x+1)(x+1)(x-4)(x+2)(x-5) ==(x-3x+1)(x-3x-4)(x-3x-10)=-30 令x-3x-4=t 則有(t+5)(t-6)t=-30 t-t-30t+30=0 即(t-1)(t-30)=0 t=1或t=±√30 當(dāng)t=1,x-3x-5=0 x=(3±√29)/2 當(dāng)t=√30,x-3x-5-√30=0 x=[3±√(29+4√30)]/2=[3±√(√24+√5)]/2=[3±(2√6+√5)]/2 當(dāng)t=-√30,x-3x-5+√30=0,x=[3±√(29-4√30)]/2=[3±(2√6-√5)]/2 綜上 x=(3±√29)/2或[3±(2√6±√5)]/2