JEE Challenger
More from Trigonometric Functions

Value of Ratio of Cotangents in a Given Triangle

Consider a triangle ABCABC with side lengths given by AB=23AB = \sqrt{23}, BC=3BC = 3, and CA=4CA = 4. Calculate the value of cot⁡A+cot⁡Ccot⁡B\frac{\cot A + \cot C}{\cot B}

Official Numerical Answer2

Step-by-Step Solution

In △ABC\triangle ABC, let the side lengths opposite to the vertices A,B,A, B, and CC be denoted by a,b,a, b, and cc respectively.

From the given information: a=BC=3a = BC = 3 b=CA=4b = CA = 4 c=AB=23c = AB = \sqrt{23}

We know that for any triangle ABCABC with area Δ\Delta, the cotangent of an angle can be expressed in terms of its sides as: cot⁡A=b2+c2−a24Δ\cot A = \frac{b^2 + c^2 - a^2}{4\Delta} cot⁡B=c2+a2−b24Δ\cot B = \frac{c^2 + a^2 - b^2}{4\Delta} cot⁡C=a2+b2−c24Δ\cot C = \frac{a^2 + b^2 - c^2}{4\Delta}

Adding cot⁡A\cot A and cot⁡C\cot C, we get: cot⁡A+cot⁡C=(b2+c2−a2)+(a2+b2−c2)4Δ=2b24Δ\cot A + \cot C = \frac{(b^2 + c^2 - a^2) + (a^2 + b^2 - c^2)}{4\Delta} = \frac{2b^2}{4\Delta}

Now, taking the ratio cot⁡A+cot⁡Ccot⁡B\frac{\cot A + \cot C}{\cot B}: cot⁡A+cot⁡Ccot⁡B=2b24Δa2+c2−b24Δ=2b2a2+c2−b2\frac{\cot A + \cot C}{\cot B} = \frac{\frac{2b^2}{4\Delta}}{\frac{a^2 + c^2 - b^2}{4\Delta}} = \frac{2b^2}{a^2 + c^2 - b^2}

Substitute the values of a2a^2, b2b^2, and c2c^2: a2=32=9a^2 = 3^2 = 9 b2=42=16b^2 = 4^2 = 16 c2=(23)2=23c^2 = (\sqrt{23})^2 = 23

Substituting these values into the ratio: cot⁡A+cot⁡Ccot⁡B=2(16)9+23−16=3216=2\frac{\cot A + \cot C}{\cot B} = \frac{2(16)}{9 + 23 - 16} = \frac{32}{16} = 2

Thus, the value of the expression is 22.