if a square + b square + c square equal to 90 and a + b + c = 20 then find the value of AB + BC + CA
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Answer:
ab + bc + ac =155
Step-by-step explanation:
(a+b+c)²=a²+b²+c²+2ab+2bc+2ac
(20)² = 90+2(ab+bc+ac)
400-90/2=ab+bc+ac
ab+bc+ac= 155
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