if a²+b²+c²=90 abd a+b+c=20 theb the calue pf 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
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