Sin4x-sin8x using a sum to product to rewrite the expression

You are assembling pieces of an iron gate to complete a fence. the finished gate will look like the one below. in order to assemble the gate it is important to under how the pieces are related. part 1: how are pies 1 and 2 in the archway related? part 2: how are the rectangular sections 5 and 6 in the center of the gate related to each other?

What is the value of x when x + 7 = 21?

Which phrase generalizes the specific terminology bolded in the text?