Question 1205070
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Any square has all four interior angles of 90 degrees each. 
Angle ADC = 90


Any equilateral triangle has each interior angle of 60 degrees.
Angle EDA = angle CDH = 60


Focus on the angles around point D.
They must add to 360 to do a full sweep or full rotation.
(angleEDH) + (angleEDA) + (angleADC) + (angleCDH) = 360
(x) + (60) + (90) + (60) = 360
x + 210 = 360
x = 360-210
x = 150


Angle EDH = 150 degrees
Sides ED and DH of triangle EDH are 4 cm each.


For triangle EDH we have the SAS (side angle side) case here, which means we can use the law of cosines to find the missing side.


d^2 = e^2 + h^2 - 2*e*h*cos(D)
(EH)^2 = (DH)^2 + (ED)^2  - 2*DH*ED*cos(angle EDH)
(EH)^2 = 4^2 + 4^2 - 2*4*4*cos(150)
(EH)^2 = 59.712813 
EH = sqrt(59.712813)
EH = 7.727407



Segment EH is roughly 7.727 cm long. Round this value however needed or however your teacher instructs.
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