Question Number 11473 by tawa last updated on 26/Mar/17

Show that the graph of  y = x^3  + 2x^2  + x + 1 , between x = − 1 and x = 2  lies entirely above the x − axis

Commented byprakash jain last updated on 28/Mar/17

y=x^3 +2x^2 +x+1  =x(x^2 +2x+1)+1  =x(x+1)^2 +1  y>0 for x>0  −1≤x≤0  x(x+1)^2 >−1  x(x+1)^2 +1>0

Answered by sm3l2996 last updated on 26/Mar/17

Commented bytawa last updated on 26/Mar/17

God bless you sir.