Examination content:
The radius ratio of the big circle and the small circle is known, so find the perimeter ratio and area ratio.
A triangle, the angle ratio is known, find the number of angles, or judge what triangle it is.
Given the time ratio of Party A and Party B, find the work efficiency ratio.
Know the relationship between one quantity and another quantity and this quantity, and find their values or ratios.
Dissolve salt in water and find out the ratio of salt, water and brine.
Judge the positive and negative proportional relationship.
Formula related to circle:
1, circular area: S=πr? ，S=π(d/2)？ . (d is the diameter and r is the radius).
2. area of semicircle: s semicircle = (π r 2)/2. (r is the radius).
3. Ring area: s great circle -S small circle = π (r 2-r 2) (r is the radius of great circle and r is the radius of small circle).
4. Circumference: C=2πr or c = π d..(d is the diameter and r is the radius).
5. The circumference of a semicircle: d+(πd)/2 or d+π r (d is the diameter and r is the radius).
6. The area of the circle where the sector is located is divided by 360 and multiplied by the angle n of the central angle of the sector, as shown below:
S=n/360×πr？ .
S=πr？ ×L/2πr=Lr/2(L is arc length and r is sector radius).