Prove that tan2a is equal to 2tana/1-tan^2a

Can someone me i’m confused. will give brainliest and a whole bunch of points

Steve wants to develop a way to find the total cost of any item including sales tax. the sales tax in his city is 6%. his friend jenna writes the expression x + 6x where x is the cost of the item. explain whether her expression is correct based on the situation.

15 there is a line that includes the point 0,10 and has a slope of 7/4. what is it’s equation in slope intercept form