Question

an isosceles triangle has congruent sides of 20cm. the base is 10cm. find the height of the triangle.​

Answer 1

Answer:

$\large\boxed{A_\triangle=25\sqrt{15}\ cm^2}$

Step-by-step explanation:

Look at the picture.

The formula of an area of a triangle:

$A_\triangle=\dfrac{bh}{2}$

b - base

h - height

We need a length of a height.

Use the Pythagorean theorem:

$leg^2+leg^2=hypotenuse^2$

We have:

$leg=5,\ leg=h,\ hypotenuse=20$

Substitute:

$5^2+h^2=20^2$

$25+h^2=400$             subtract 25 from both sides

$h^2=375\to h=\sqrt{375}\\\\h=\sqrt{(25)(15)}\\\\h=\sqrt{25}\cdot\sqrt{15}\\\\h=5\sqrt{15}\ cm$

Calculate the area:

$A_\triangle=\dfrac{(10)(5\sqrt{15})}{2}=\dfrac{50\sqrt{15}}{2}=25\sqrt{15}\ cm^2$