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Q.
If a + b + c = 13, a2+b2+c2=69 then find the ab + bc + ca :
A.
10
B.
30
C.
50
D.
70
View Answer
Correct choice: C
Explanation:
(a+b+c)2=a2+b2+c2+2(ab+bc+ca) 2(ab+bc+ca)=(a+b+c)2−(a2+b2+c2)=169−69=100=(ab+bc+ca)=50
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