Answers

2015-05-10T22:38:03+05:30
(a+b+c)^2=(7)^2=49
a^2+b^2+c^2+(ab+bc+ca)=49
a^2+b^2+c^2+2(20)=49
a^2+b^2+c^2=49-40
so answer is 9
0
2015-05-11T11:47:27+05:30
Using 
(a+b+c)² formula
(a+b+c)²=a²+b²+c²+2ab+2bc+2ac
(a+b+c)²-2ab-2bc-2ac=a²+b²+c²
(7)²-2(ab+bc+ac)=a²+b²+c²
49-2(20)=a²+b²+c²
therefore, a²+b²+c²=9
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