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Show that the the triangle is isosceles

Posted July 23rd, 2009 by alpha
in

In a triangle ABC,if$ Cos A=\frac{sinB}{2sinC} $, then show that the the triangle is isosceles.

$$\frac{b^2+c^2-a^2}{2bc}=\frac{2R\sin B}{4R\sin C}=\frac{b}{2c}$$
$$c^2=a^2$$
$$c=a$$
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Comments

answer

On July 24th, 2009 Structure says:
$$\frac{b^2+c^2-a^2}{2bc}=\frac{2R\sin B}{4R\sin C}=\frac{b}{2c}$$
$$c^2=a^2$$
$$c=a$$

~~THANK YOU ~~

On July 26th, 2009 alpha says:

-------------------x----------------------------
``Old theorems never die; they turn into definitions.''
----E. Hewitt

''ALPHA" =)

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