Question

If a + b + c = 7 and a2+ b2+ c2= 9,then find ab + bc + ca.

Answer 1

Answer:

a+b+c=7

(a+b+c)²=7²

(a+b+c)²=49

(a+b+c)²=a²+b²+c²+2(ab+BC+CA)

49=9+2(ab+BC+CA)

49-9=2(ab+BC+CA)

40=2(ab+BC+CA)

20=ab + bc + ca