4. If a+b+c=7 and ab+bc+ca=20 then find a² +6²+ C².
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18
Answer:
9
Step-by-step explanation:
(a+b+c)²=a²+b²+c²+2ab+2bc+2ca (a+b+c)²-2ab-2bc-2ca=a²+b²+c²
(7)²-2(ab+bc+ca) =a²+b²+c²
(7)²-2(20) = a²+b²+c²
49-40 = a²+b²+c²
a²+b²+c²=9
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