Hello,
The formula for finding the area of a circular region is:

then:

With the two radius it is formed an isosceles triangle, so, we must obtain its area, but first we obtain the height and the base.

Now we can find its area:
![A_{2}=2* \frac{b*h}{2} \\ \\ A_{2}= [r*sen(40)][r*cos(40)]\\ \\A_{2}= r^{2}*sen(40)*cos(40)](https://tex.z-dn.net/?f=A_%7B2%7D%3D2%2A%20%5Cfrac%7Bb%2Ah%7D%7B2%7D%20%20%5C%5C%20%20%5C%5C%20A_%7B2%7D%3D%20%5Br%2Asen%2840%29%5D%5Br%2Acos%2840%29%5D%5C%5C%20%20%5C%5CA_%7B2%7D%3D%20r%5E%7B2%7D%2Asen%2840%29%2Acos%2840%29)
The subtraction of the two areas is 100cm^2, then:
Answer: r= 1.59cm
Answer:
Part 1) 
Part 2) 
Step-by-step explanation:
Part 1)
we know that
The perimeter of triangle is equal to the sum of its length sides
so

Part 2)
we know that
The area of triangle is given by the formula

we have

substitute

First you convert the percentage into a decimal. 18% to 0.18, then you multiply that decimal to the price of the item being discounted and bam, you have your price.