Question

if a+b+c=11 and a^2+b^2+c^2=21 find the value of ab+bc+ca​

Answer 1

Answer:

a + b + c = 11

a^2 + b^2 + c^2 =21

Therefore ,

ab + bc + ca = 50

Step-by-step explanation:

We know

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

Putting the value given in the question

we get,

11^2 = 21 + 2( ab + bc + ca )

=> 121 = 21 + 2( ab + bc + ca )

=> 121 - 21 = 2 ( ab + bc + ca )

=> 100 = 2 ( ab + bc + ca )

=> ab + bc + ca = 100/2

=> ab + bc + ca = 50

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