How to ritate a tringle using a protractor to 90?

How to rotatae a triangle using a protractor?

Mind your spelling please, and do not double post, this is not a chatting site.

Draw a line from the vertices of the triangle to the centre of rotation. Put your protractor on the drawn line and measure the angle you need to rotate. Make a mark at the required angle and draw a line from the centre of rotation on the mark you just did. Measure the length from the vertex (of the triangle from which you initially draw a line) to the centre and measure the same length to the line you just drew. That point is the rotated point of the triangle. Repeat with the other vertices.

It's difficult to explain through the internet, so, why not ask your teacher?