I need help with 8-13 I have 0 clue how to do it and I need to graduate soon

The diagram shows a 7cm by 6cm rectangle based pyramid. all the diagonal sides - ta, tb, tc and td are length 10cm. m is midpoint of rectangular base. work out height mt to 1 decimal place

What is the measure of ac? 5 units 13 units 26 units 39 units

Find the cosine function that is represented in the graph.