Hasil dari (1^3)-(2^3)+(3^3)-(4^3)+(5^3)-(6^3)+...+(49^3-50^3)

Berapakah hasil dari (1^3)-(2^3)+(3^3)-(4^3)+(5^3)-(6^3)+...+(49^3-50^3)

Solusinya:

(a-b)^3=a^3-3a^2b+3ab^2-b^3
a^3-b^3=(a-b)^3+3a^2b-3ab^2
a^3-b^3=(a-b)^3+3ab(a-b)
1^3-2^3=(1-2)^3+3.1.2(1-2)= -1-3(1.2)
3^3-4^3=(3-4)^3+3.3.4(3-4)= -1-3(3.4)
5^3-6^3=(5-6)^3+3.5.6(5-6)= -1-3(5.6)
......................................................
49^3-50^3=(49-50)^3+3.49.50(49-50)= -1-3(49.50)
Sehingga:
1^3-2^3+3^3-4^3+...+49^3-50^3 =25(-1)-3(1.2+3.4+5.6+7.8+.....49.50)
=-25-3(2+12+30+56+....+2450)
Selanjutnya tinggal mencari(2+12+30+56+....+2450). Coba lanjutkan dulu.