If a^2 + b^2 + c^2 = 90 and a + b + c = 20 then find the value
of ab + bc + ca.
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Answer: (a+b+c)² = a²+b²+c²+2(ac+bc+ca)
(20)² = 90+2(ab+bc+ca)
400 = 90+ 2(ab+bc+ca)
400-90 =2(ab+bc+ca)
310 = 2(ab+bc+ca)
.ab+bc+ca = 155
Step-by-step explanation:
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