Question

area of right - angled triangles
find the area of this right - angled triangle.
because the area of this triangle is half the area of the rectangle shown,
we can find the area of the rectangle and then divide it by two to find the area
of the triangle.
so the area=(8 cm×4 cm)÷2
=32 cm²÷2 = 16 cm²
area = 16 cm²
find the area of these right - angled triangles.
© dorling kindersley limited 2010 dk

Explanation:

Step1: Recall area formula

The area formula for a right - angled triangle is $A=\frac{1}{2}\times base\times height$, where base and height are the two sides forming the right - angle.

Step2: Calculate for first triangle

For the triangle with base $b = 12$ cm and height $h = 5$ cm, $A=\frac{1}{2}\times12\times5=30$ $cm^{2}$.

Step3: Calculate for second triangle

For the triangle with base $b = 10$ cm and height $h = 3$ cm, $A=\frac{1}{2}\times10\times3 = 15$ $cm^{2}$.

Step4: Calculate for third triangle

For the triangle with base $b = 9$ cm and height $h = 2$ cm, $A=\frac{1}{2}\times9\times2=9$ $cm^{2}$.

Step5: Calculate for fourth triangle

For the triangle with base $b = 14$ cm and height $h = 4$ cm, $A=\frac{1}{2}\times14\times4 = 28$ $cm^{2}$.

Step6: Calculate for fifth triangle

For the triangle with base $b = 6$ cm and height $h = 5$ cm, $A=\frac{1}{2}\times6\times5=15$ $cm^{2}$.

Step7: Calculate for sixth triangle

For the triangle with base $b = 8$ cm and height $h = 6$ cm, $A=\frac{1}{2}\times8\times6=24$ $cm^{2}$.

Step8: Calculate for seventh triangle

For the triangle with base $b = 12$ cm and height $h = 6$ cm, $A=\frac{1}{2}\times12\times6 = 36$ $cm^{2}$.

Step9: Calculate for eighth triangle

For the triangle with base $b = 20$ cm and height $h = 3$ cm, $A=\frac{1}{2}\times20\times3=30$ $cm^{2}$.

Step10: Calculate for ninth triangle

For the triangle with base $b = 7$ cm and height $h = 4$ cm, $A=\frac{1}{2}\times7\times4 = 14$ $cm^{2}$.

Answer:

30 $cm^{2}$, 15 $cm^{2}$, 9 $cm^{2}$, 28 $cm^{2}$, 15 $cm^{2}$, 24 $cm^{2}$, 36 $cm^{2}$, 30 $cm^{2}$, 14 $cm^{2}$