Question

代数式y平方减3y加6的值等于5,求代数式y三次方减8y加7的值？

Answer 1

y^2-3y+6=5
y^2-3y+1=0
y^2-3y=-1
y^2=3y-1
y^2*y=(3y-1)*y=3y^2-y
y^3-8y+7
=3y^2-y-8y+7
=3y^2-9y+7
=3(y^2-3y)+7
=-1*3+7
=4,2,4,0,