7^(n+2)-3^(n+2)+7^n-3^n=7^n*(7^2+1)-3^n*(3^2+1)=50*7^n-10*3^n=10*(5*7^n-3^n)
........................
2(5y-3)=y^2-5*(1,2-2y)
10y-6=y^2-6+10y
10y-10y-y^2=-6+6
-y^2=0
y^2=0
y=0