I'm working through the 'how to solve it' book and i'm a bit lost about solving this problem - I can do algebra alright but transforming x^4-13x^2+36=0 to (2x^2)^2-2(2x^2)13+144=0 doesn't seem to follow a simple rule of algebra. It's not like simply replacing x with x^2. Anyone help with what I'm missing? #math #maths #teahyourselfcs #algebra #howtosolveit