Question

if a^2+b^2+c^2=90 and a+b+c=20 find ab+bc+ca

Answer 1

hope it will help you....
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Answer 2

hey your ans is here

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given

a2+b2+c2=90
a+b+c=20

to find
Ab+BC+ca

now apply the identity
(a+b+c)2=a2+b2+c2+2(Ab+BC+ca)
(20)2=90+2(Ab+BC+ca)
400=90+2(Ab+BC+ca)
400-90/2=Ab+BC+ca
155=Ab+BC+ca
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