Question

if a+b+c=15 and a2+b2+c2= 25 find the value of ab+bc+ac​

Answer 1

a + b + c = 15

Squaring both sides,

( a + b + c )^2 = 15^2

a^2+b^2+c^2+2ab+2bc+2ca = 225

25 + 2ab + 2bc + 2ac = 225

25 + 2 ( ab + bc + ac ) = 225

2 ( ab + bc + ac ) = 225 - 25

2 ( ab + bc + ac ) = 200

ab + bc + ac = 200/2

ab + bc + ac = 100

Ans. ab + bc + ac = 100