デジブ用英語
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- 5 (1) Since ABCD is a square, \EAB = 90±.
In 4ABE,
25± + 90± + \AEB = 180± ) \AEB = 65±
4A0 BE is obtained by folding 4ABE
The sum of the degree measures of the interior angles of a triangle is
180±.
along BE, we have
\AEB = \A0 EB = 65±
) \DEA0 = 180± ¡ (65± + 65± ) = 50±
(2) Since BA = BA0 , 4ABA0 is an isosceles triangle.
6 (1) The Pythagorean theorem gives us
(BC) = (AB) + (AC) (BC)2 = 62 + 42 (BC)2 = 52 p BC = § 52
2 2 2
Pythagorean theorem
Since BC > 0, p BC = 52 p = 2 13 p ) BC = 2 13 cm (2) Since \BAC = So, the radius is
1 £ (BC) 2 p ) 13 cm
Three sides of a right-angled triangle relate:
90±
and the triangle is inscribed in a circle, then side
c2 = a2 + b2
BC becomes the diameter of the circle.
What’s the point?
If point B and point C are opposite ends of a diameter and point A is on the circumference, then \BAC will always be 90±. Conversely, in 4ABC , if \BAC is
90± and a circle circumscribes 4ABC,
then side BC will always be the diameter.
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