Question

If a+b+c=20. a + b = 90, find the value of ab + bc+ca​

Answer 1

Step-by-step explanation:

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

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

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

310/2=ab+bc+ca

155=ab+bc+ac