An angle less than 90 degrees.

This is an angle less than 90 degrees because the vertex is an acute angle and wen

it's acute the number has to be less than 90 degrees .This we'll help you a lot because

if you don't now your angles of course you don't now how to measure .And you may think that

It's not important ,well it's time to practice because you can even lose your job.now that you now it's important you have to study