Question

If a + b + c = 9 and ab + bc + ca = 40 then find a2 + b2 + c2

Answer 1

(a+ b+ c)^2 = 9 ×9 =81
a 2 + b2+c2 + 2 ( ab + bc + ca) = 81
a2+ b2+ c2 + 2×40 =81
a2 + b2 + c2 = 1

Answer 2

hey your ans is here
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given
a+b+c=9
Ab+BC+ca=40
a2+b2+c2=?
now using identity
(a+b+c)2=a2+b2+c2+2(Ab+BC+ca)
putting values
(9)2=a2+b2+c2+2(40)
81=a2+b2+c2+80
81-80=a2+b2+c2
1=a2+b2+c2
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:-)