question_answer 1)

Find the circumference of the circles with the following radius \[\left( \text{Take  }\!\!\pi\!\!\text{  = }\frac{\text{22}}{\text{7}} \right)\]:                 (a) 14 cm                              (b) 28 mm                           (c) 21 cm.

Answer:

                (a) 14 cm                 \[\text{r =14 cm}\] \[\therefore \] Circumference of the circle                 \[\text{= 2 }\!\!\pi\!\!\text{ r = 2  }\!\!\times\!\!\text{  }\frac{\text{22}}{\text{7}}\text{  }\!\!\times\!\!\text{  14 = 88 cm}\]                 (b) 28 mm                 \[\text{r = 28 mm}\] \[\therefore \]  Circumference of the circle                 \[=2\pi r=2\times \frac{22}{7}\times 28=176\text{mm}\]                 (c) 12 cm                 \[\text{r = 21 cm}\] \[\therefore \]  Circumference of the circle                 \[\text{= 2 }\!\!\pi\!\!\text{ r = 2  }\!\!\times\!\!\text{  }\frac{\text{22}}{\text{7}}\text{  }\!\!\times\!\!\text{  21 = 132 cm}\].