Given A-B = - 2, B-C = 5, find the value of a ^ 2 + B ^ 2 + C ^ 2-ab-ac-bc
a-b=-2,b-c=5
Then A-B + B-C = - 2 + 5
Then a-c = 3
a^2+b^2+c^2-ab-ac-bc
=(2a^2+2b^2+2c^2-2ab-2ac-2bc)÷2
=(a²-2ab+b²+b²-2bc+c²+a²-2ac+c²)÷2
=[(a-b)²+(b-c)²+(a-c)²]÷2
=(4+25+9)÷2
=19
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