Question

If a+b-c=5 and a²+b²+c²=29 find the value of ab-bc-ca

Answer 1

here is your answer,

⇒first, by using the formula( a+b+c)²= a²+b²+c²+2ab+2bc+2ca

⇒ given that a+b+c=5 and a²+b²+c²=29

⇒ (a+b+c)²= a²+b²+c²+2ab+2bc+2ca

⇒(5)²= 29+2(ab+bc+ca)

⇒ 25= 31(ab+bc+ca)

⇒ ab+bc+ca= 31-25

⇒ab+bc+ca= 6

⇒hope it helps→←

Answer 2

(a+b-c)^2=5^2
a^2+b^2+c^2+2 (ab-bc-ca)=25. (Substitute values)
29+2 (ab-bc-ca)=25
2 (ab-bc-ca)=25-29
(ab-bc-ca)=-4/2=-2