A B C D is a square with side length 8 . Let M and N be the midpoints of sides B C and C D , respectively, and let θ = ∠ M A N . Then what is the value of sin θ + cos θ ?
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I wish I can take a pic of my solution and upload here - editor doesn't work for me. Step 1 - just draw a square and state the lengths ,place the midpoints and use simple surds to find the sides of the triangles formed. Step 2 - for the triangle within the square - MN = 4 ROOT 2 and AM is root 80 .The perpendicular bi sector of the triangle (height) is 6 root 2 . step 3 - use the sine rule a/sinA =b/sin B and find for sin x = 3/5 then just draw a right angle using sin x =3/5 and find cos x = 4/5 add and you will get 7/5 Guys can we upload pics as solutions ?
To upload pics, you can load them onto Imgur / Flick, and then use markdown to pull up the picture. For example, the code
! [image] (https://ds055uzetaobb.cloudfront.net/avatars-2/resized/80/e6e66b8981c1030d5650da159e79539a.3fe78221256b7adcfbcc8b609332e38a.jpg)
with spaces removed will produce
image
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Right angle D A B is expressible as 2 π = θ + 2 arctan ( 4 / 8 ) ⇒ θ = 2 π − 2 arctan ( 1 / 2 ) . Thus:
sin θ + cos θ = sin ( 2 π − 2 arctan ( 1 / 2 ) ) + cos ( 2 π − 2 arctan ( 1 / 2 ) ) ;
or cos ( 2 arctan ( 1 / 2 ) ) + sin ( 2 arctan ( 1 / 2 ) ) ;
or 2 cos 2 ( arccos ( 2 / 5 ) − 1 + 2 sin ( arcsin ( 1 / 5 ) cos ( arccos ( 2 / 5 ) ;
or 2 ( 5 4 ) − 1 + 2 ( 5 1 ) ( 5 2 ) ;
or 5 1 2 − 1 ;
or 5 7 .
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the angle at MAN is 45 take sin 45 and cos 45 u will get 7/5