Question

a + b + c is equal to 12 and a square + b square + c square equal to 64 then the value of AB + BC + CA is​

Answer 1

Answer:

$a {}^{2} + b { }^{2} + c {}^{2} =( a + b + c) {}^{2} - 2(ab + bc + ca)$

so u'll get

$64 = 12 {}^{2} - 2(ab + bc + ca) \\ - 2(ab + bc + ca) = 64 - 144 \ \: = - 80 \\ \\ (ab + bc + ca) = 80 \div 2 \\ = 40 \\ so \: answer \: is \: 40$