Question

If a^2 + b^2 + c^2 =90 and a+ b+ c = 20 .Then ab + bc + ca is ​

Answer 1

Answer:

Step-by-step explanation:

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

20^2=90+2(ab+bc+ac)

400-90=2(ab+bc+ac)

ab+bc+ac=310/2

               =155