Applicare la formula: $\left(a+b\right)^2$$=a^2+2ab+b^2$, dove $a=2r\sin\left(x\right)$, $b=-\cos\left(x\right)$ e $a+b=2r\sin\left(x\right)-\cos\left(x\right)$
Applicare la formula: $\left(a+b\right)^2$$=a^2+2ab+b^2$, dove $a=\cos\left(x\right)^2$, $b=-\sin\left(x\right)^2$ e $a+b=\cos\left(x\right)^2-\sin\left(x\right)^2$
Moltiplicare il termine singolo $r^2$ per ciascun termine del polinomio $\left(\cos\left(x\right)^{4}-2\cos\left(x\right)^2\sin\left(x\right)^2+\sin\left(x\right)^{4}\right)$