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Solution & Area of Oblique Triangle Textbook of Algebra and Trigonometry for Class XI
The Law of Cosine o a 2 = b2 + c 2 - 2bc cos a b2 + c 2 - a 2 o cos a = 2bc
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o b 2 = c 2 + a 2 - 2ca cos b c2 + a 2 - b2 o cos b = 2ca
o c 2 = a 2 + b 2 - 2ab cos g a 2 + b2 - c 2 o cos g = 2ab
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The Law of Sine a b c = = sin a sin b sin g
o
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The Law of Tangent
( a -b ) ( )
a - b tan 2 o = a + b tan a + b 2
( b -g ) ( )
( g -a ) ( )
b - c tan 2 o = b + c tan b +g 2
c - a tan 2 o = c + a tan g +a 2
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Half Angles Formulas o sin
a = 2
( s - b )( s - c ) bc
s(s - a) a = 2 bc a ( s - b )( s - c ) o tan = 2 s(s - a) o cos
where s =
o sin
b = 2
( s - c )( s - a )
o sin
ca
s ( s - b) b = 2 ca b ( s - c )( s - a ) o tan = 2 s ( s - b)
g = 2
( s - a )( s - b ) ab
s( s - c) g = 2 ab g ( s - a )( s - b ) o tan = 2 s(s - c)
o cos
o cos
a+b+c 2
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Area of Triangle ( = D ) 1 1 1 o D = bc sin a = ca sin b = ab sin g 2 2 2 2 2 a sin b sin g b sin g sin a c 2 sin a sin b o D = = = = 2sin a 2sin b 2sin g s ( s - a )( s - b )( s - c )
o D =
(Hero’s Formula)
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Circum Radius ( = R ) a b c o R = = = 2sin a 2sin b 2sin g
o R =
abc 4D
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In Radius ( = r ) o r =
D s
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Escribed Circle o r1 =
D s-a
o r2 =
D s -b
o r3 =
D s-c
……………………………………………………………………………………………………………………………………… Made By: Atiq ur Rehman
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