Mathematics: Perimeter and Area 1 You should be able to calculate: ❖ Perimeter and area of rectangle ❖ Perimeter and area of triangle ❖ Perimeter and area of compound shapes derived from the above The Perimeter is the total length of all sides of a shape. Perimeter and area of a rectangle A rectangle has 4 sides, so the perimeter is equal to the length of all 4sides combined Perimeter = a + a + b + b = 2a + 2b = 2(a+b) Area of rectangle = a x b (length x width) Perimeter and area of triangle The perimeter of a rectangle is equal to the length of all three sides. Inmany cases, Perimeter = a + b + c However, we may not always know the length all 3 sides of the triangle. Ifthe triangle is a right-angled triangle, we can use the pythagoras theorem
to deduce the length of any side (given that we already know the lengthof 2 sides) Pythagoras Theorem: C 2 = a 2 + b 2 The equation can be re-arranged to ﬁnd the length of any side: Perimeter and area of compound shapes Finding the perimeter of compound shapes is extremely simple, you justneed to add up the length of all sides. However, sometimes there may be a few sides with no length, but wecan ﬁnd the length by doing some simple subtracting. For example, thecompound shape on the right, we can ﬁnd the length of the top side bydoing 10 – 6 = 4. Finding the area is also extremely simple, all you have to do is split thecompound shapes into individual shapes which you could then calculate.For example, for this compound shape we can split it into 2 rectangles, aand b (red line). Afterwards, we can just add up the area of the tworectangles to ﬁnd the area of the compound shape.