Kirsty says, “When you double the size of an acute angle, you always get an obtuse angle.” Explain why Kirsty is not correct.
Acute angles are angles which are less than 90 degrees. And obtuse angles are angles which are greater than 90 and less than 180 degrees. We know that 90 divided by two is 45. So we could double anything less than 45. And we would still have an acute angle.
So to explain why Kirstie is not correct, we could say that we could double any acute angle which is less than 45 degrees. And the total would be less than 90 degrees. Angles less than 90 degrees are also acute.