Applicare la formula: $\left(a+b+c\right)^2$$=a^2+b^2+c^2+2ab+2ac+2bc$, dove $a=c$, $b=e\cos\left(x\right)$ e $c=-g\cos\left(y\right)$

Applicare la formula: $ab$$=ab$, dove $ab=2\cdot -1cg\cos\left(y\right)$, $a=2$ e $b=-1$

Applicare la formula: $ab$$=ab$, dove $ab=2e\cdot -1g\cos\left(x\right)\cos\left(y\right)$, $a=2$ e $b=-1$

Applicare la formula: $\left(-x\right)^n$$=x^n$, dove $x=g\cos\left(y\right)$, $-x=-g\cos\left(y\right)$ e $n=2$

Applicare la formula: $\left(ab\right)^n$$=a^nb^n$, dove $a=g$, $b=\cos\left(y\right)$ e $n=2$