=a? -2ab+b? +b? -2ac+c? +c? -2ac+a?
=2a? +2b? +2c? -2ab-2bc-2ac
(2) Given a-b= 10 and b-c=5, use the conclusion in (1) to find the value of A +b +c -ab-bc-ca.
∫a-b = 10 b-c = 5
∴a-c= 15
Square of a+square of b+square of c-ab-BC-ca.
=(2a? +2b? +2c? -2ab-2bc-2ac)÷2
=[(a-b)? +(b-c)? +(A-C)? ]÷2
=( 10? +5? + 15? )÷2
=( 100+25+225)÷2
=350÷2
= 175