Olympiad workbook
- Exam
- Olympiad workbook
- Subject
- IOQM
- Chapter
- Properties of Triangles
Olympiad workbook · IOQM · Properties of Triangles
If 15 and 9 are lengths of two medians of a triangle, what is the...
If 15 and 9 are lengths of two medians of a triangle, what is the maximum possible area of the triangle to the nearest integer?
Correct answer
90
Step-by-step solution
Area of

\begin{aligned} & \text { S }=\frac{11+x}{2} \\ & \begin{aligned} \text { Area }= & \sqrt{\frac{11+x}{2}\left(\frac{11+x}{2}-x\right)\left(\frac{11+x}{2}-5\right)\left(\frac{11+x}{2}-6\right)} \\ & =\sqrt{\frac{11+x}{2}\left(\frac{11-x}{2}\right)\left(\frac{x+1}{2}\right)\left(\frac{x-1}{2}\right)} \\ & =\sqrt{\frac{\left(121-x^2\right)\left(x^2-1\right)}{16}}\end{aligned} \\ & \text { Let } \mathrm{y}=\frac{\left(121-\mathrm{x}^2\right)\left(\mathrm{x}^2-1\right)}{16} \\ & \text { For } \mathrm{max} \text { area } \frac{\mathrm{dy}}{\mathrm{dx}}=0 \\ & -2 \mathrm{x}\left(\mathrm{x}^2-1\right)+\left(121-\mathrm{x}^2\right) 2 \mathrm{x}=0 \\ & -\mathrm{x}^2+1+121-\mathrm{x}^2=0\end{aligned}\triangle \mathrm{ABC}=6 \times 15=90$
\begin{aligned} & \text { S }=\frac{11+x}{2} \\ & \begin{aligned} \text { Area }= & \sqrt{\frac{11+x}{2}\left(\frac{11+x}{2}-x\right)\left(\frac{11+x}{2}-5\right)\left(\frac{11+x}{2}-6\right)} \\ & =\sqrt{\frac{11+x}{2}\left(\frac{11-x}{2}\right)\left(\frac{x+1}{2}\right)\left(\frac{x-1}{2}\right)} \\ & =\sqrt{\frac{\left(121-x^2\right)\left(x^2-1\right)}{16}}\end{aligned} \\ & \text { Let } \mathrm{y}=\frac{\left(121-\mathrm{x}^2\right)\left(\mathrm{x}^2-1\right)}{16} \\ & \text { For } \mathrm{max} \text { area } \frac{\mathrm{dy}}{\mathrm{dx}}=0 \\ & -2 \mathrm{x}\left(\mathrm{x}^2-1\right)+\left(121-\mathrm{x}^2\right) 2 \mathrm{x}=0 \\ & -\mathrm{x}^2+1+121-\mathrm{x}^2=0\end{aligned}\triangle \mathrm{ABC}=6 \times 15=90$