2ax-10ay+5by-bx
=2a(x-5y)-b(x-5y)
=(2a-b)(x-5y)
由a-b=5,b-c=3得a-c=8
又(a-b)^2=a^2=b^2-2ab
(a-c)^2=a^2=c^2-2ac
(c-b)^2=c^2=b^2-2bc
等式两边分别相加,
得(a-b)^2+(a-c)^2+(c-b)^2=2a^2+2b^2+2c^2-2ab-2ac-2bc
a^2+b^2+c^2-ab-ac-bc=(25+9+64)/2=49
2ax-10ay+5by-bx
=2a(x-5y)-b(x-5y)
=(2a-b)(x-5y)
由a-b=5,b-c=3得a-c=8
又(a-b)^2=a^2=b^2-2ab
(a-c)^2=a^2=c^2-2ac
(c-b)^2=c^2=b^2-2bc
等式两边分别相加,
得(a-b)^2+(a-c)^2+(c-b)^2=2a^2+2b^2+2c^2-2ab-2ac-2bc
a^2+b^2+c^2-ab-ac-bc=(25+9+64)/2=49