Let Δ P Q R be a triangle. Let a → =   Q R → ,     b → =   R P…

Let ΔPQR be a triangle. Let a= QR,  b= RP and c= PQ. If a=12, b=43 and b  c=24, then which of the following is (are) true ?
  1. c22- a=12
  2. c22+ a=30
  3. a × b+ c × a=483
  4. a  b= -72

Solution

a=12, b=43, b.c=24
a+b+c=0 (Sides of triangle)
b+c=-a
b+c.b+c=-a.-a
b2+c2+2b.c=a2
48+c2+2×24=122
c2=48
c22-a=482-12=12
c22+a=482+12=36
a×b+c×a=a×b-a×c
=a×b-c
a=-b-c
=-b-c×b-c=b-c×b+c
=2b×c
=2b2c2-b.c2=248×48-242
=2×244-1=483
a+b=-c
a+b.a+b=-c.-c
a2+b2+2a.b=c2
a.b=-a22=-1222=-72

Asked in: JEE Advanced 2015 (Paper 1)

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