If a + b + c = 13, a^2 + b^2 + c^2 = 69, then what is the value of (ab + bc + ca).

Simplification Test 5

Question : 32 of 40

Marks: +1, -0

a + b + c = 13

a^2 + b^2 + c^2 = 69

, then what is the value of

(ab + bc + ca)

Solution:

(a + b + c)^2

= a^2 + b^2 + c^2 + 2(ab + bc + ca)

∴ ab + bc + ca

={ (a + b + c)^2-(a^2 + b^2 + c^2) }/2

={13^2-69}/2={169-69}/2

=100/2=50

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