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Question from saravanan, a student:

Dear Sir ,
I felt difficulty solving the following problem . So please help me .

a+b+c=7
ab+bc+cd= 20
what is a^2+b^2+c^2 ?

Saravanan,

Did you mean $ab + bc + ac=20?$

If so, then start with the following:

\[(a + b + c)^2 = 7^2\]

Expand this and see if you can make any substitutions.

Cheers,
L. Dame and RD

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