New Zealand
Level 8 - NCEA Level 3

# Evaluate Areas Using Geometry

Lesson

If a curve or a hybrid function looks like a familiar geometric shape when we graph it, we are easily able to find the area bounded by the curve(s) and the $x$x-axis.

##### Example 1

To find the shaded area on this graph we can simply calculate the area of a right triangle.

Area=$\frac{3\times6}{2}$3×62

Area=$9$9 $units^2$units2

##### Example 2

To find the shaded area bounded by this curve and the x-axis we can find the area of a semicircle.

Area=$\frac{\pi\times4^2}{2}$π×422

Area=$25.13$25.13 $units^2$units2

##### Example 3

How would we find the area bounded by the three lines and the $x$x-axis below?

We don't need to break it up into three different sections, although we could. Instead we can find the area of a trapezium.

Area=$\frac{2\left(2+5\right)}{2}$2(2+5)2

Area=$7$7 $units^2$units2

#### Worked Examples

##### Question 1

Consider the function drawn below:

1. Calculate geometrically, the area bounded by the curve and the $x$x-axis over $0\le x\le4$0x4.

##### Question 2

Find the exact value of $\int_0^{12}f\left(x\right)dx$120f(x)dx geometrically, where $y=f\left(x\right)$y=f(x) is graphed below.

##### Question 3

Find the exact value of $\int_{-6}^6\sqrt{36-x^2}dx$6636x2dx geometrically.

##### Question 4

The function $f\left(x\right)$f(x) is defined as:

 $2x$2x if $0\le x\le3$0≤x≤3 $f\left(x\right)$f(x) $=$= $6$6 if $33 1. Graph$f\left(x\right)$f(x) on the axis below. Loading Graph... 2. Hence, calculate geometrically the area bounded by the curve and the$x\$x-axis.

### Outcomes

#### M8-11

Choose and apply a variety of differentiation, integration, and antidifferentiation techniques to functions and relations, using both analytical and numerical methods

#### 91579

Apply integration methods in solving problems