need help

**calculus_jy** · June 17th 2007, 11:24 PM

1)in a triangle, if A=2B prove that a^2=b^2 + bc
2)in a triangle, if a+c=2b prove that cot(C/2) = 3 tan(A/2)
PS please dont use calculus to solve!

**topsquark** · June 18th 2007, 03:42 AM

Originally Posted by calculus_jy

1)in a triangle, if A=2B prove that a^2=B^2 + bc

In general there is a difference between the variables "b" and "B." When referring to triangles B tends to represent the angle across from the side of length b. The first question, with $a^2 = B^2 + bc$ then, makes no sense. Even if you meant b = B, there are a variety of triangles with the property $A = 2B$ with different values of c so the proposed equality need not be true.

-Dan

**Krizalid** · June 18th 2007, 09:33 AM

Originally Posted by calculus_jy

1)in a triangle, if A=2B prove that a^2=B^2 + bc

Mmmm

Given $\triangle{ABC}$ where $\measuredangle~A=2\cdot\measuredangle~B$ then $a^2=b(b+c)$

It's a well known property.

**calculus_jy** · June 19th 2007, 02:01 AM

sorry for wasting ur time,
i made a mistake in typeing B when i meant b and i already know that in a triangle AB=c AC=b and BC= a,

when i posted it, i actually want to c the prove, however, i hav already proven it, so dont worry about it

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