Respuesta :

Answer:

Step-by-step explanation:

[tex]\sum^{12}_{r=1} r^2 = \frac{12(12+1)(2*12+1)}{6}= A[/tex]

[tex]\sum_{r=3}^{12}= \sum_{r=1}^{12} - (r_1+r_2)[/tex]

[tex]r_1= 1^2[/tex]

[tex]r_2= 2^2[/tex]

you do your math!!