Question

If
$a + b -c = 4 \: and \: a {}^{2} + b {}^{2} + c {}^{2} = 38$
then find ab-bc-ca

plz answer my question ​

Answer 1

Answer:

ab - bc - ca = - 11

Step-by-step explanation:

a + b - c = 4

[squaring both sides]

(a + b - c)² = 16

=> a² + b² + c² + 2(ab - bc - ca) = 16

=> 2(ab - bc - ca) = 16 - 38

=> ab - bc - ca = 22/2

=> ab - bc - ca = - 11