Thread: proof

i have got the question...

in triangle ABC, the lengths of the sides a, b, c have the relation 2b equals to a + c.

i. prove that 2 sin B equals sin A + sin C.
this part i have done...
but i can t handle the next part, which is

ii hence, show that cos {（A - C）/2 } = 2 sin（B / 2）

Originally Posted by ling_c_0202

i have got the question...

in triangle ABC, the lengths of the sides a, b, c have the relation 2b equals to a + c.

i. prove that 2 sin B equals sin A + sin C.
this part i have done...
but i can t handle the next part, which is

ii hence, show that cos {（A - C）/2 } = 2 sin（B / 2）

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thanks for your reply. however, there is a minor mistake.

but i can still get the answer. thanks a lot