Question

If a2+b2+c2=83 and a+b+c=15 then the value of ab+bc+ca is

A) 69 B) 70 C) 71 D) 72

Answer 1

Answer:

81

Step-by-step explanation:

a²+b²+c²=83,

a+b+c=15,

On squaring both sides, we get

a²+b²+c²+2(ab+bc+ca)=225

• 83+2(ab+bc+ca)=225
• 2(ab+bc+ca)=142

ab+bc+ca=71