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Olympiad workbook
Exam
Olympiad workbook
Subject
IOQM
Chapter
Properties of Triangles

Olympiad workbook · IOQM · Properties of Triangles

In a triangle ABC , the median AD (with D on BC ) and the angle...

In a triangle ABC , the median AD (with D on BC ) and the angle bisector BE (with E on AC ) are perpendicular to each other. If AD=7\mathrm{AD}=7 and BE=9\mathrm{BE}=9, find the integer nearest to the area of triangle ABCA B C.In a triangle ABC , the median AD (with D on BC ) and the angle bisector BE (with E on AC ) are perpendicular to each

Correct answer

47

Step-by-step solution

In a triangle ABC , the median AD (with D on BC ) and the angle bisector BE (with E on AC ) are perpendicular to each
Let ADA D and BEB E meet at FF Now ∠ABF=∠FBD=B2\angle \mathrm{ABF}=\angle \mathrm{FBD}=\frac{\mathrm{B}}{2} and ∠AFB=∠BFD=30∘\angle \mathrm{AFB}=\angle \mathrm{BFD}=30^{\circ} and BF is common to triangles ABF and BFD hence the two triangles are Cengruent so AF=FD=72\mathrm{AF}=\mathrm{FD}=\frac{7}{2} Also, AB=BD,⇒AB:BC=1:2\mathrm{AB}=\mathrm{BD}, \Rightarrow \mathrm{AB}: \mathrm{BC}=1: 2 ⇒AE:EC=1:2\Rightarrow \mathrm{AE}: \mathrm{EC}=1: 2 So area of triangle ABC=3A B C=3 (Area of △ABE\triangle A B E ) =3(12×AF×BE)=32×72×9=1894=47.25\begin{aligned} & =3\left(\frac{1}{2} \times \mathrm{AF} \times \mathrm{BE}\right) \\ & =\frac{3}{2} \times \frac{7}{2} \times 9=\frac{189}{4}=47.25 \end{aligned} Hence nearest integer = 47
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