Each side of an equilateral triangle measures 9cm. find the height, h, of the triangle.

You can make the equilateral triangle into a right triangle by cutting it in half. So, your sides would be 4.5, 9, and x.
Using Pythagorean Theorem, you know that a^2 + b^2 = c^2.

The 'a' would be equal to 9, and 9^2 is equal to 81.

B is equal to 4.5, and 4.5^2 is 20.25.

So, you have the following:

81 + 20.25 = c^2

And that makes 'c' equal to 101.25.
The square root of 101.25 is approximately equal to 10.06.

So now you know the height, 10.06.

I got 7.8 (rounding to the nearest tenth)
i used the smas formula but i got : (4.5*4.5+x^2=9*9)
so, 20.25+x^2=81
then, x^2= 60.75 (i got 60.75 from subtracting 20.25 from 81)
fonal square root both sides

The answer would be (c)