![]() ![]() 5 Worksheets to measure the angles with Pre-printed Protractors. The intersection of the diameter and the chord at 90 degrees can be very close to the centre and so the two lengths coming from the point of intersection to the radius are assumed to be equal, but they aren’t. Worksheet on identifying angles as Acute, Obtuse, Right or Straight angles. Incorrect assumption of isosceles triangles.This also includes the inverse trigonometric functions. The incorrect trigonometric function is used and so the side or angle being calculated is incorrect. The missing side is calculated by incorrectly adding the square of the hypotenuse and a shorter side, or subtracting the square of the shorter sides. The only case of this is when both angles are 90^o. Opposite angles are the same for a cyclic quadrilateralĪs angles in the same segment are equal, the opposing angles in a quadrilateral are assumed to be equal.Angle at the centre is supplementary to opposing angleĪs the shape is a quadrilateral, the angle at the centre is assumed to be supplementary and add to 180^o.The angle ABC = 56^o as it is in the alternate segment to the angle CAE. Here, angle ABC is incorrectly calculated as 180 - 56 = 124^o. The angle is taken from 180^o which is a confusion with opposite angles in a cyclic quadrilateral. Opposite angles in a cyclic quadrilateral.The measurement worksheet will produce two problems per page. Top tip: Use arrows to visualise which way the alternate segment angle appears: This Measurement Worksheet is great for practicing reading and using a protractor to measure angles. The chord BC is assumed to be parallel to the tangent and so the angle ABC is equal to the angle at the tangent. Parallel lines (alternate segment theorem).The angle at the circumference is assumed to be 90^o when the associated chord does not intersect the centre of the circle and so the diagram does not show a semicircle. They should total 90^o as the angle in a semicircle is 90^o. The angles that are either end of the diameter total 180^o as if the triangle were a cyclic quadrilateral. The angles are all very close or equal to 90 degrees, so pupils have to come up with a way (using the gridlines) to decide. Look out for isosceles triangles and the angles in the same segment. If you find having the angle colored helpful, you can use markers. Notice that the MLN is now colored in the diagram below. MLN is the angle formed by points M, L, and N with a vertex at point L. First, make sure that you correctly identify the angle in question. Make sure that you know when two angles are equal. Example: Use a protractor to find the measure of MLN in the diagram below. Direct students to use the inner scale if the angle opens to the right, and the outer scale if the angle opens to the left, so they can easily measure the angles. The angle at the centre is always larger than the angle at the circumference (this isn’t so obvious when the angle at the circumference is in the opposite segment). Angles can be measured using the inner or outer scale of the protractor. Make sure you know the other angle facts including:īy remembering the angle at the centre theorem incorrectly, the student will double the angle at the centre, or half the angle at the circumference. Below are some of the common misconceptions for all of the circle theorems: ![]()
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