## iwanttogotostanford one year ago HELP W? ACT PREP: The figure below shows 2 tangent circles such that the 10-centimeter diameter of the smaller circle is equal to the radius of the larger circle. What is the area, in square centimeters, of the shaded region? DRAWN BELOW

1. iwanttogotostanford

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2. zepdrix

3. iwanttogotostanford

the larger circle only

4. zepdrix

Inside the big circle, but outside the small one? ah ok

5. iwanttogotostanford

yep

6. zepdrix

That's not too bad :) That's simply the area of the big circle - area of the small circle

7. zepdrix

You'll have to recall your area formula: $$\large\rm A=\pi r^2$$ What is the area of the larger circle? Are you able to figure that out based on the information given?

8. iwanttogotostanford

yes! so it would be two equations, one pi (10)^2 and then the other pi(10)^2?

9. zepdrix

Ooo careful! :) They didn't actually tell us the radius of the smaller circle.

10. iwanttogotostanford

oh yeah ok so what do i do?

11. zepdrix

You have to remember the relationship bebtween diameter and radius.

12. iwanttogotostanford

13. zepdrix

Ok good :o Half of 10 is 5. So that gives us the r that we want to use for the smaller circle.

14. iwanttogotostanford

yes

15. zepdrix

You had your first equation correct, which corresponded to the area of the larger circle $$\large\rm \pi(10)^2$$

16. zepdrix

So the smaller one, which we've corrected, should be $$\large\rm \pi(5)^2$$ ya? :o

17. iwanttogotostanford

yes

18. zepdrix

Square those numbers, then subtract the smaller one from the larger one

19. iwanttogotostanford

i forget do i use pi in the equation orr just leave it until the end

20. iwanttogotostanford

ok nevermind for my final answer i got 75pi

21. zepdrix

yay good job \c:/

22. iwanttogotostanford

thanks