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In an isosceles triangle \mathrm{A B C}, the coordinates of the point \mathrm{B} and \mathrm{C} on the base \mathrm{BC} are respectively \mathrm{(1,2)} and \mathrm{(2,1)}. If the equation of the line \mathrm{A B} is \mathrm{y=2 x}, then the equation of the line \mathrm{ A C} is

Option: 1

y=\frac{1}{2}(x-1)


Option: 2

y=\frac{x}{2}


Option: 3

y=x-1


Option: 4

2 y=x+3


Answers (1)

best_answer

Slope of B C =\frac{1-2}{2-1}=-1

A B=A C, \, \, \therefore \angle A B C=\angle A C B

\Rightarrow\left|\frac{2+1}{1+2(-1)}\right|=\frac{m+1}{1+m(-1)} \Rightarrow \frac{m+1}{1-m}=|-3| \Rightarrow \frac{m+1}{1-m}= \pm 3 \Rightarrow   m=2, \frac{1}{2} .

\text { But slope of } A B \text { is } 2 ; \quad \therefore \quad m=\frac{1}{2}                           (Here m is the gradient of the line

Equation of the line AC is y-1=\frac{1}{2}(x-2) \Rightarrow x-2 y=0 \text { or } y=\frac{x}{2}

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