Answer:
<h2>
Yes, this is a right triangle.</h2>
Step-by-step explanation:
Hypotenuse always have the highest number than base and perpendicular.
Hypotenuse ( h ) = 15
Base ( b ) = 9
Perpendicular ( p ) = 12
Let's see whether the given triangle is a right triangle or not
Using Pythagoras theorem:

Plugging the values,

Evaluate the power

Calculate the sum

Hypotenuse is equal to the sum of perpendicular and base.
So , we can say that the given lengths of the triangle makes a right triangle.
Hope this helps..
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So to find the mean you add them all together and divide by the number of numbers there is so 11+15+19+17+23+20+17+18+21=174 and there are 10 numbers so it would be 174/10 which is 17.4 so you answer is 17.4