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help needed any one who knows math will help
- Thread starter munir
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Do u know the sine rule nd do u know how to label the sides corresponding to angles.I just wanted to know so that i move forward to explain the cosine rule .I will be using Q3b in june 2009 as an example!
okay. lets say you have a triangle, so here is the rule as we all know it, (ac)squared = (bc) squared + (ab) squared now the cosine rule will help you in this, (the 2 is the squared)
(bc or ac or ab)2 = (bc or ab or ac)2 + (ab or ac or bc)2 x 2 x (bc or ab or ac) x (ab or ac or bc) x cos angle, lets say you have a triangle, you need the base, the base is ac , but you cant do the rule up so it is (lets take my numbers =p)
(ac)2 = 2(2) + 3(2) x 2 x 2 x 3 x cos the angle between the line 2 and 3 (that is 2 and 3 meters) hope i helped
(bc or ac or ab)2 = (bc or ab or ac)2 + (ab or ac or bc)2 x 2 x (bc or ab or ac) x (ab or ac or bc) x cos angle, lets say you have a triangle, you need the base, the base is ac , but you cant do the rule up so it is (lets take my numbers =p)
(ac)2 = 2(2) + 3(2) x 2 x 2 x 3 x cos the angle between the line 2 and 3 (that is 2 and 3 meters) hope i helped
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what i tell 2 everyone is whenever finding which rule to use see what is involved in the question,i.e.,given and that 2 be found.
Cosine rule is used when a question involves 3 sides and1 angle
specifically=>to find a side when an angle opp. to that side and the other 2 sides given OR to find angle when all the 3 sides are given.
the formula is a^2=b^2 + c^2 - (2bc cos A)
Q3b June 2009 one more thing in such questions label the sides ON THE FIG. to avoid errors
so u will mark on the diagram QP as r , PR as q , QR as p
u want to find p so angle P should be known which is 43.3(ans of (a) )
eqn. => p^2 = q^2 + r^2 - (2qr cos P)
p^2=14^2+10^2 - (2 x 14 x 10 cos 43.3)
p^2 = 296 - (280 cos 43.3)
p^2 = 296-203.78
p^2 = 92.22
p = root of 92.22 = 9.603 =rounded=>9.60cm
hope this helps if any doubt donot hesitate good luck
Cosine rule is used when a question involves 3 sides and1 angle
specifically=>to find a side when an angle opp. to that side and the other 2 sides given OR to find angle when all the 3 sides are given.
the formula is a^2=b^2 + c^2 - (2bc cos A)
Q3b June 2009 one more thing in such questions label the sides ON THE FIG. to avoid errors
so u will mark on the diagram QP as r , PR as q , QR as p
u want to find p so angle P should be known which is 43.3(ans of (a) )
eqn. => p^2 = q^2 + r^2 - (2qr cos P)
p^2=14^2+10^2 - (2 x 14 x 10 cos 43.3)
p^2 = 296 - (280 cos 43.3)
p^2 = 296-203.78
p^2 = 92.22
p = root of 92.22 = 9.603 =rounded=>9.60cm
hope this helps if any doubt donot hesitate good luck
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i think u r mistaken im 100% sure that its a^2=b^2 + c^2 - (2bc cos A)
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zaid it's -2bc not *2bc
maths angel is right
maths angel is right
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no problem but be careful in the exam!