∵a-b=b-c=3/5
∴a-c=6/5
a²+b²+c²=1
2a²+2b²+2c²=2
2a²+2b²+2c²-2ab-2bc-2ac=2-2ab-2bc-2ac
(a-b)²+(b-c)²+(a-c)²=2-2ab-2bc-2ac
(3/5)²+(3/5)²+(6/5)²-2=-2ab-2bc-2ac
9/25+9/25+36/25-2=-2ab-2bc-2ac
-2(ab+bc+ac)=54/25-50/25
∴ab=-2/25
∵a-b=b-c=3/5
∴a-c=6/5
a²+b²+c²=1
2a²+2b²+2c²=2
2a²+2b²+2c²-2ab-2bc-2ac=2-2ab-2bc-2ac
(a-b)²+(b-c)²+(a-c)²=2-2ab-2bc-2ac
(3/5)²+(3/5)²+(6/5)²-2=-2ab-2bc-2ac
9/25+9/25+36/25-2=-2ab-2bc-2ac
-2(ab+bc+ac)=54/25-50/25
∴ab=-2/25