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The radius of the inner circle is sqrt(9) = 3. The radius of the outer circle is therefore 3*3 = 9.

The equation for the outer circle is then x^2 + y^2 = 9^2 = 81. (This is an application of Pythagoras' theorem a^2 + b^2 = c^2 in a right-angled triangle by the way)

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Q: The equation of the inner circle is x2 plus y2 equals 9 The radius of the outer circle is three times the radius of the inner circle What is the equation of the outer circle?
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The equation of the inner circle is x2 plus y2 equals 9 The radius of the outer circle is twice the radius of the inner circle What is the equation of the outer circle?

x^2+y^2=36


What is the length of a chord of the circle x2 plus y2 equals 72 which is tangent to the circle x2 plus y2 equals 18?

The circles are concentric with centre (0,0). The radius of the outer circle is sqrt(72), that of the inner circle is sqrt(18). By Pythagoras, the length of the semichord is sqrt(72 - 18) = sqrt(54) units. Therefore the chord is 2*sqrt(54) = 6*sqrt(6) = 14.679 units (approx).


The area of a circular ring is 90 if the radius of the outer circle forming the ring is 9 what is the radius of the inner circle of the ring assuming the circles forming the ring have same center?

Outer radius = a; inner radius = b; then area of the ring = pi (a2 - b2) = 90, where pi = 22/7. In view of a = 9, we have b2 = 81 - [90 x 7 / 22], the positive square root of which gives b.


What are the angles of a regular 4 pointed star?

As far as I know, there is no "regular" 4 pointed star. However, if you have a 4 pointed star, you can draw a circle through it's inner points and a second circle around its outer points. If we say that the inner circle has radius "r" and the outer circle has radius "R", that the angle, "a", of the star's points are: a = atan(2r / (R√2 - r) If the outer circle is twice as big as the inner circle, this becomes: a = atan(2r / (2r√2 - r) = atan(2 / (2√2-1) = 47.5°


How do you calculate the area of a ring?

Treat the ring as a circle. Area equals pi (3.14) times the radius squared. Whether you take the inner of the ring or the outer of the ring, rather depends on how thick the ring is - inner is probably best as that should loosely match the thickness of the finger on which the ring will eventually sit.

Related questions

The equation of the inner circle is x2 plus y2 equals 9 The radius of the outer circle is twice the radius of the inner circle What is the equation of the outer circle?

x^2+y^2=36


The equation of the inner circle is x2 plus y2 equals 4 the radius of the outer circle is four times the radius of the inner circle write the equation of the outer circle?

The inner circle is x2 + y2 = 4. The radius of the inner circle is the square root of 4, which is 2. To find the radius of the outer circle, multiply 2 times 4. The radius of the outer circle is 8. Square 8 (82 or 8 x 8) to find the number to put into the equation of the outer circle. This is 64. The equation for the outer circle is x2 + y2 = 64.


How do you divide a circle into 8 equal parts using 3 lines?

Draw two diameters perpendicular to each other. Draw a smaller circle with the same centre such that the radius of the inner circle is 'r' and the radius of the outer circle is 'r√2.' [Or, the radius of the outer circle is R and the radius of the inner circle is R/√2.]


How do you find the approximate circumference of the inner circle?

it depends on what the radius is if they give you one


What do you mean by internal radius?

It's the radius of a circle or sphere WITH A SHELL(or Thickness); like if an Lid on a jar had a diameter of 11mm across on the outside (top of lid); and was ONE mm thick, then the inside radius would be 5. ie; 11mm outer diameter, minus (-) 1mm thickness (aka; or shell) equals (=) 10mm (inner) diameter; which is a 5mm radius.


How do you draw a circle with any radius in which i and o are intriour and exteriour?

Continue or follow the inner or outer trajectory of the radius arc line in either, or both, directions until it meets itself. The i will have a center point which is at a fixed distance from the arc, equal to one half of the radius of the finished circle, and which will thereby prove the circle.


What is the length of a chord of the circle x2 plus y2 equals 72 which is tangent to the circle x2 plus y2 equals 18?

The circles are concentric with centre (0,0). The radius of the outer circle is sqrt(72), that of the inner circle is sqrt(18). By Pythagoras, the length of the semichord is sqrt(72 - 18) = sqrt(54) units. Therefore the chord is 2*sqrt(54) = 6*sqrt(6) = 14.679 units (approx).


Perimeter of the sector?

A track 7m wide consists of two concentric circles. The circumference of the inner circle is 440m. Find, 1) the radius of the outer circle 2) the circumference of the outer circle.


The area of a circular ring is 90 if the radius of the outer circle forming the ring is 9 what is the radius of the inner circle of the ring assuming the circles forming the ring have same center?

Outer radius = a; inner radius = b; then area of the ring = pi (a2 - b2) = 90, where pi = 22/7. In view of a = 9, we have b2 = 81 - [90 x 7 / 22], the positive square root of which gives b.


What are the angles of a regular 4 pointed star?

As far as I know, there is no "regular" 4 pointed star. However, if you have a 4 pointed star, you can draw a circle through it's inner points and a second circle around its outer points. If we say that the inner circle has radius "r" and the outer circle has radius "R", that the angle, "a", of the star's points are: a = atan(2r / (R√2 - r) If the outer circle is twice as big as the inner circle, this becomes: a = atan(2r / (2r√2 - r) = atan(2 / (2√2-1) = 47.5°


How do you calculate the area of a ring?

Treat the ring as a circle. Area equals pi (3.14) times the radius squared. Whether you take the inner of the ring or the outer of the ring, rather depends on how thick the ring is - inner is probably best as that should loosely match the thickness of the finger on which the ring will eventually sit.


How many square meters of brick pavement must be laid for a 4 meter wide walk around a circular flower bed 22 meters in diameter?

This problem is solved by first computing the area of the larger circle - the outside of the walk in this case. This circle has a diameter of 22 + 8 m, therefore a radius of 15m. The inner circle has a diameter of 22m - as given - a radius of 11m. You subtract the area of the inner circle from that of the larger circle. I'll leave you to do the math.