If the area of triangle \(A B C\) is \(b^2-(c-a)^2\), then \(\tan B=\)
If the area of triangle \(A B C\) is \(b^2-(c-a)^2\), then \(\tan B=\)
- 1
- \(\frac{13}{15}\)
- \(\frac{1}{4}\)
- \(\frac{8}{15}\)
Solution
Given,
\(\begin{aligned}
& \text { Area of a triangle }=b^2-(c-a)^2 \\
\Delta & =b^2-(c-a)^2 \\
& =(b+c-a)(b-c+a) \\
& =(2 s-2 a)(2 s-2 c) \\
& =4(s-a)(s-c)
\end{aligned}\)
Now \(\sqrt{s(s-a)(s-b)(s-c)}=4(s-a)(s-c)\)
\(\begin{aligned}
& \Rightarrow \quad \sqrt{s(s-b)}=4 \sqrt{(s-a)(s-c)} \\
& \Rightarrow \quad \frac{1}{4}=\sqrt{\frac{(s-a)(s-c)}{s(s-b)}} \Rightarrow \frac{1}{4}=\tan \left(\frac{B}{2}\right) \\
& \therefore \tan B=\frac{2 \tan \left(\frac{B}{2}\right)}{1-\tan ^2\left(\frac{B}{2}\right)}=\frac{2 \times \frac{1}{4}}{1-\frac{1}{16}}=\frac{\frac{1}{2}}{\frac{15}{16}} \\
& =\frac{1}{2} \times \frac{16}{15}=\frac{8}{15}
\end{aligned}\)
Asked in: AP EAMCET 2019 (22 Apr Shift 1)
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