How would I do this? I know from the graph that the roots are -0.9 and 0.9 but how do I show this??? Any help much appreciated.
If you may use that is continuous, it shouldn't be that hard: must reach all values in .
(look up theorem of Bolzano. I believe there's other even other names for that)
given that and it follows that there exists a with such that .
You can use this argument twice to show the existence of 2 roots (without necessarily finding them).