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MHT CET · Maths · Properties of Triangles

In a triangle \(\mathrm{ABC}\), with usual notations \(\angle A=60^{\circ}\), then \(\left(1+\frac{a}{c}+\frac{b}{c}\right)\left(1+\frac{c}{b}-\frac{a}{b}\right)=\)

  1. A \(\frac{3}{2}\)
  2. B \(\frac{1}{2}\)
  3. C 1
  4. D 3
Verified Solution

Answer & Solution

Correct Answer

(D) 3

Step-by-step Solution

Detailed explanation

\(\left(1+\frac{a}{c}+\frac{b}{c}\right)\left(1+\frac{c}{b}-\frac{a}{b}\right)=\frac{a+b+c}{c} \times \frac{b+c-a}{b}\) \(=\frac{(b+c)^2-a^2}{b c} \)
\( =\frac{b^2+c^2-a^2+2 b c}{b c}=2\left(\frac{b^2+c^2-a^2}{2 b c}\right)+2 \)
\( =2 \cos A+2=2 \cos 60^{\circ}+2=2 \times \frac{1}{2}+2=3\)