若a=√17-1,求a5+2a4_17a3_a2+18a-17...急等...
1个回答

a^5+2a^4-17a³-a²+18a-17

=a^4(a+2)-17a³-a²+18a-17

=a³*a*(√17-1+2)-17a³-a²+18a-17

=a³*(√17-1)(√17+1)-17a³-a²+18a-17

=a³*(17-1)-17a³-a²+18a-17

=17a³-a³-17a³-a²+18a-17

=-a³-a²+18a-17

=-a³-2a²+a²+18a-17

=-a²(a+2)+a²+18a-17

=-a*a*(√17-1+2)+a²+18a-17

=-a*(√17-1)*(√17+1)+a²+18a-17

=-a(17-1)+a²+18a-17

=-17a+a+a²+18a-17

=a²+2a+1-18

=(a+1)²-18

=(√17-1+1)²-18

=17-18

=-1