Theory of cubic equation question

[Curious3141]

sighh sigh sighj sigh sigh sigh sigh why didn't i see that ...

(1+4x)^2 = 1 + 8x + 16x^2...

VERY GOOD. Finally. OK, now just simplify and group the terms.

Remember to expand the LHS correctly too.

BTW, if you're working in the variable 'y', you should use that throughout, otherwise it's confusing (and actually wrong).

 

[lionely]

it is x³ -14x²+x-1

 

[Curious3141]

it is x³ -14x²+x-1

Not quite. Every coefficient is right except the one for the x term. You must have made a mistake, show your exact work.

A bit of a cheat, but you can test your answer here: http://www.gyplan.com/eqcubic_en.html

And, not to belabour the point, what you wrote is still not an equation! You MUST put the '=0'.

 

[lionely]

lol... x^3 -14x^2-7x-1

 

[Curious3141]

lol... x^3 -14x^2-7x-1

Still not an equation. Just an expression. But all the coefficients are right.

 

[lionely]

looooooool OKAY HERE IT IS x^3 -14x^2-7x-1 = 0!

 

[Curious3141]

looooooool OKAY HERE IT IS x^3 -14x^2-7x-1 = 0!

GREAT!