Question

if a+b+c=7and ab+bc+ca=20,find the value of a^2+b^2+c^2​

Answer 1

Answer:

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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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Answer 2

Answer:

(a+b+c)2= a2+b2+c2+2(ab+bc+ca)

72 = a2+b2+c2+ 2×20

49 = a2+b2+c2 + 40

49 - 40 = a2+b2+c2

.·. 9 = a2+b2+c2

Ans : 9

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