Question

If p+q+r=12 and p^2 +q^2+r^2=50, find pq+ qr +pr.

Answer 1

Answer:

p+q+r=12

(p+q+r)^2=(12)^2

p^2 +q^2+r^2+2pq+2qr+2pr=144      [(a+b+c)^2=a^2+b^2+c^2+2ab+2bc+2ac)]

50+2pq+2qr+2pr=144                        (given  in question)

2pq+2qr+2pr=144-50

2(pq+qr+pr)=94

pq+qr+pr=94/2

[pq+qr+pr=47]

47 is the answer