Triangle: known the angle between the two sides, calculate the area? Formula and formula analysis, detailed explanation emergency

Triangle: known the angle between the two sides, calculate the area? Formula and formula analysis, detailed explanation emergency

In the triangle ABC, if the opposite sides of the three interior angles a, B and C are a, B and C respectively, the triangle area is:
S=(1/2)absinC=(1/2)bcsinA=(1/2)acsinB

Given the length of a corner and its two sides, what is the formula for finding the area of a triangle?

s=(1/2) ab.sinc

Use a piece of triangle paper to deduce the calculation formula of triangle area, and write the derivation process below
I see what they wrote: make two arbitrary triangle pieces, make the same height, cut open,
Put the same parts together and you get two rectangles,
The formula for calculating the area of a triangle can be derived by calculating half of the area of two rectangles
What's the final answer? Nothing else

It can be proved that if you want to make an arbitrary one that is not easy to spell, you can make one of the same size, cut it from the top corner along the height, and put it together with the original triangle to form a rectangle. For example, the first picture. If you want to use one, you have to cut it on the original basis, and then put it together into a square or parallel edge. For example, the second picture and the third picture

Panda accountant of forest fruit store found that the money was less than 100 yuan when checking out. After verification, he found that a figure on a receipt was polluted, which became? 52.72 yuan. The person who handled the receipt said: at the beginning of the month, 72 people bought peaches, and each person bought the same amount of peaches and paid the same amount of money. I wrote the receipt to them collectively, but accidentally soiled it, This sum is 152.72 yuan. Is Lao Huang right?
Why? How much should it be?
It is uncertain that the payment order is a single person collection order

Answer: 72 people, each person's money as much, that the total money must be divided by 72
From 152.72 to 952.72, only 252.72 can be divided by 72
Therefore, the money should be 252.72 yuan