Question 87620
1. {{{ f(x)=-7x^4+343x^2 }}}
{{{ f(x)=-7x^2(x^2-49) }}}
{{{ f(x)=-7x^2(x+7)(x-7) }}}


2. think of {{{ x^4-16x^2+15 }}} as {{{ y^2-16y+15 }}} where {{{y=x^2}}}. You can factorise this quadratic in y by looking and then re-write y as x^2 for each solution and find out what x is for each.


cheers
Jon