Trouble with angles and lengths

Geometry Level pending

Here, A B P = 3 0 \angle ABP=30^{\circ} , A B Q = 6 7 \angle ABQ=67^{\circ} , B A P = 6 0 \angle BAP=60^{\circ} , B A Q = 4 6 \angle BAQ=46^{\circ} , P Q R = 80. 6 \angle PQR=80.6^{\circ} , A B = 200 m AB=200 m and P R = 266.36 m PR=266.36 m . O O is the incenter of the triangle P Q R PQR . If x x is the distance of O O from R Q RQ then we can write a < x < a + 1 a<x<a+1 . What is the value of a a (in meter) ?


The answer is 54.

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1 solution

Fazla Rabbi
Apr 25, 2014

Our first target is to find out another side of P Q R \triangle PQR
In A B P \triangle ABP ,
A P B = 18 0 ( 3 0 + 6 0 ) \angle APB = 180^{\circ} -(30^{\circ} + 60^{\circ}) = 9 0 90^{\circ}
Hence, cos 3 0 = B P 200 \cos 30^{\circ} = \frac {BP}{200}
B P = 200 cos 3 0 = 173.2 m BP = 200 \cos 30^{\circ} = 173.2m


Again, In A B Q \triangle ABQ ,
Hence, B Q sin 4 6 = 200 sin 6 7 \frac {BQ}{\sin 46^{\circ}}= \frac {200}{\sin 67^{\circ}}
B Q = 156.3 m BQ = 156.3m

Then in P B Q \triangle PBQ ,the cosine rule gives,
P Q 2 = B P 2 + B Q 2 2 B P B Q cos 9 7 PQ^{2} = BP^{2} + BQ^{2} - 2*BP*BQ \cos97^ {\circ } = ( 173.2 ) 2 + ( 156.3 ) 2 2 ( 173.2 ) ( 156.3 ) ( . 1219 ) = (173.2)^{2} + (156.3)^{2} - 2(173.2)(156.3)(-.1219)
Hence, P Q = 247 m PQ = 247m

Now,In P Q R \triangle PQR ,
266.36 sin 80. 6 = 247 sin P R Q \frac{266.36}{\sin 80.6^{\circ}} = \frac{247}{\sin PRQ}
or, sin P Q R = . 91486455 \sin PQR = .91486455
or, P Q R = sin 1 ( . 91486455 ) \angle PQR = \sin^{-1} ({ .91486455 })
so, P Q R = 66.1 9 \angle PQR = 66.19^{\circ}
Again P Q R \triangle PQR ,
R P Q = 18 0 ( 80. 6 + 66.1 9 ) \angle RPQ = 180^{\circ} - (80.6^{\circ} + 66.19^{\circ})
so, R P Q = 33.2 1 \angle RPQ = 33.21^{\circ}

Now,In P Q R \triangle PQR ,
266.36 sin 80. 6 = R Q sin 33.2 1 \frac{266.36}{\sin 80.6^{\circ}} = \frac{RQ}{\sin 33.21^{\circ} }
so, R Q = 147.87 RQ = 147.87
The area of the P Q R \triangle PQR = 1 / 2 r p sin P Q R 1/2 * r*p* \sin PQR
= 1 / 2 247 147.87 sin 80. 6 1/2 * 247*147.87* \sin 80.6^{\circ}
= 18016.73 18016.73
Let x x is the distance of O O from p p or q q or r r
Area of P O Q = 1 / 2 r x \triangle POQ = 1/2* r*x
Area of R O P = 1 / 2 q x \triangle ROP = 1/2* q*x
Area of R O Q = 1 / 2 p x \triangle ROQ = 1/2* p*x

Thus the total area of P Q R = 1 / 2 x ( p + q + r ) = 300.615 x \triangle PQR = 1/2*x(p+q+r)=300.615*x
But this area is 18016.73 18016.73 . Herce, the area of O O from R Q , x = 18016.73 300.615 = 54.5 RQ , x= \frac {18016.73}{300.615} =\boxed{54.5}
We can write a < 54.5 < a + 1 a<54.5<a+1 54 < 54.5 < 54 + 1 54<54.5<54+1 or 54 < 54.5 < 55 54<54.5<55
SO, a = 54 a= \boxed{54}

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