# Find the resultant of two vectors of magnitude 5 & 3 and making angle 60degree between them? Here if we use triangle law of vector addition i.e we just add the two vectors we get resultant as 8 BUT if we use parallelogram law answer comes out to 7. (R= √P²+Q²+2PQcos∅) How is this possible? Please explain. I will be very thankful. According to me it should not matter which law we use. Resultant should be same. PLEASE EXPLAIN IITIANS please reply today itself. It’s Very important

Aakash
110 Points
9 years ago
In Triangle law of vector addition we not just add vector and Both laws are same and formula from both laws is same. We can simply add if angle between them is 0. Just go through the theory again to understand concept well
Ali Hasan
33 Points
9 years ago
But the answer is not same for both triangle and prallelogram law. By triangle law answer is 8 and by parallelogram law answer is 8
Ali Hasan
33 Points
9 years ago
Sorry by parallelogram law answer is 7. Resultant should be the same in both the case right?
Ali Hasan
33 Points
9 years ago
Of course i will approve but clear my concept.

Shubham Singh
199 Points
9 years ago
triangle law does not mean just simply adding the magnitude.
u should use the law which u r comfortable with.
Ali Hasan
33 Points
9 years ago
Okay then. The answer given in my textbook is 7 but I am of course more comfortable in triangle law as we just have to add the two vectors and I get 8. Now what. Just explain this to me that how is triangle law different from parallelogram law. A parallelogram is made up of two triangles only. Triangle law should be applicable in parallelogram. There should be NO parallelogram law. Now that’s not possible. There is some basic concept behind it which some IITian can tell me. IITians REPLY. WHy are IITians not replying.
Ali Hasan
33 Points
9 years ago
OKAY SHUBHAM SINGH. If triangle law does not mean JUST adding magnitude then what does it mean?
Tanmay
22 Points
9 years ago
simply u can use the formula for findind the resultant that is A2+ B2 +2ABcos theta whole in root so it comes 25 + 9+2×5×3×cos60 whole root that gives u 7
Tanmay
22 Points
9 years ago
simply u can use the formula for findind the resultant that is A2+ B2 +2ABcos theta whole in root so it comes 25 + 9+2×5×3×cos60 whole root that gives u 7