若a*a+3a-1=0,则a*a*a+5a*a+5a+18=?可将平方立方写成简写

来源:学生作业帮助网 编辑:作业帮 时间:2024/11/27 07:42:56
若a*a+3a-1=0,则a*a*a+5a*a+5a+18=?可将平方立方写成简写
x){ѽ4Q+Q8Q@iL 7چO?tgv>_ $|1 &H P5O{7'YM5,n *01ƃ&j kbWqx!V qpQp~qAb4l#{zOYd⧭KmrfӝMؔ>؊x`sulXbqzhjk HSg!t H i!P|

若a*a+3a-1=0,则a*a*a+5a*a+5a+18=?可将平方立方写成简写
若a*a+3a-1=0,则a*a*a+5a*a+5a+18=?可将平方立方写成简写

若a*a+3a-1=0,则a*a*a+5a*a+5a+18=?可将平方立方写成简写
即a²+3a=1
原式=a³+3a²+2a²+5a+18
=a(a²+3a)+2a²+5a+18
=a×1+2a²+5a+18
=2a²+6a+18
=2(a²+3a)+18
=2×1+18
=20

20,用代入法降幂

∵a²+3a-1=0
∴a²+3a=1
a³+5a²+5a+18
=(a³+3a²)+(2a²+6a)-a+18
=a(a²+3a)+2(a²+3a)-a+18
=a×1+2×1-a+18
=a+2-a+18
=20