3 Order of Operations
In the formulae used so far you have substituted the given values into the formula and then multiplied them together. As multiplication is commutative, the order that it is carried out does not matter. But if more more than just multiplication is required then it is necessary to be more precise.
The area of a circle is calculated using the formula A=pr²
p is the number 3.14159265 to 8 decimal places
r is the radius of the circle : r² means that the radius is multiplied by itself and this must be done before multiplying by p.
| So the area of this circle is A=pr² A=p x 5² A= 78.54cm² to 2 decimal places |
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To work out the area of a
fraction of a circle, the formula needs to be suitably
modified. Eg the area of a semi-circle with radius of 8cm A=pr²÷2 A=p x 8² ÷ 2 A=p x 64 ÷ 2 A= 100.53cm² to 2 d.p. |
3A Work out the areas of these circles, giving the answers correct to 2 decimal places.
1. Radius 6cm 2. Radius 9cm 3. Radius 70cm
3B Work out the area of:-
1. A semi-circle with radius 3cm. . 2. A quarter-circle with radius 7cm 3. A third of a circle with radius 10cm
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The area of the this shape has to be worked out by working out the area of each rectangle (for which we have the formula A=lw) and then adding these two areas together. This can be written in one formula; A=LW+lw Note that L is a different number from l and that W is a different number from w. So :- A=LW+lw A=(5x4)+(3x1) ......... Multiplication is carried out before addition, but brackets used to emphasise this. A= 20 + 3 A = 23cm² |
| 3C
Use the above formula to calculate the area of each of these shapes. |
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