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Lesson Example Discussion Quiz: Class Homework

Example

Title: Area of Triangle

Grade: 1400-a Lesson: S3-L2

Explanation: Hello Students, time to learn examples. Let us take turns and read each example. Explain each step. Pay special attention to steps and pictures and communicate in your own words.

Examples:

Find the area of a triangle having base is 18cm and height is 12cm.

Step 1a

Given height(h) = 12cm

Base of a triangle(b) = 18cm

Therefore, area of a triangle = \$1/2 b*h\$

⇒ \$(18\times12)/2\$

⇒ \$216/2\$

⇒ \$108\$sq.cm

Explanation: If the height of a triangle is 12cm, and the base is 18cm, the area of the triangle is 108 sq.cm as calculated using the formula: \$1/2 bh\$.

Find the area of an equilateral triangle of side 12 cm. \$\sqrt 3 = 1.73\$.

Step 2a

Given the side of a triangle = 12cm

Area of an equilateral triangle = \$\sqrt 3/4\$ a² square units

⇒ \$\sqrt 3/4 \times 12 \times 12\$

⇒ \$\sqrt 3/4 \times 144\$

⇒ \$\sqrt 3 * \cancel144^36/\cancel4^1\$

⇒ \$1.73 \times 36\$

⇒ 62.28 cm²

Explanation: If the side of an equilateral triangle is 12cm, then the area of an equilateral triangle is 62.28 cm².

Find the height of a triangle whose area is 420 cm² and base is 60 cm.

Step 3a

The given area of a triangle(a) = 420 cm²

The base of a triangle(b) = 60 cm

Therefore, height of a triangle = \$(2 \times a)/b\$

⇒ \$(2 \times 420)/60\$

⇒ 14cm

Explanation: If the area of a triangle is 420 cm², and the base of a triangle is 60 cm, the height of a triangle is 14cm as calculated using the formula \$(2\times a/b)\$.