Diagonals

Calculate the length of the diagonals of the rhombus if its side is long 5 and one of its internal angle is 80°.

Correct result:

u1 =  6.43
u2 =  7.66

Solution:

u12=a2+a2−2aacos⁡80∘ u12=2a2−2a2cos⁡80∘ u1=a2(1−cos⁡80∘)=6.43
 β=180∘−80∘=100∘ u22=a2+a2−2aacos⁡100∘ u22=2a2−2a2cos⁡100∘ u2=a2(1−cos⁡100∘)=7.66

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