7. If a+b+c=6 and a²+b²+c²=20, find ab+bc+ca?
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Ans is 12
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Answer:
By the formula we know that, (a+b+c)² = a²+ b²+ c²+2ab+ 2bc+2ca
on putting values we get,
(6)² = 20 + 2(ab+bc+ca)
36 - 20 = 2(ab+bc+ca)
16 = 2(ab+bc+ca)
(ab+bc+ca) = 16 / 2 = 8
Your answer is 8
It is 100% right ✔ answer
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