the measure of the obtuse angle of a rhombus is twice the measure of its acute angle. if the length of each side is 10cm, determine the length of each diagonal of the rhombus. express your answer in surd form.
Answers
measure of the obtuse angle of a rhombus is twice the measure of its acute angle.
Answer:
You mean “What are the lengths”—a rhombus has two diagonals and they are unequal unless the rhombus is a square.
If there’s an obtuse angle of 110 degrees (in fact two of them) there are also acute angles of 70 degrees.
The diagonal opposite each angle can be obtained from the cosine rule
d21=102+102–2×10×10cos(70)=200(1−cos(70) , d22=102+102+2×10×10cos(70)=200(1+cos(70) .
However, notice that we can write these in terms of the sine or cosine of 35 degrees. In fact it is easier to consider the right triangles that the diagonals divide the rhombus into.
d1=2×10sin(35)=11.47 , d2=2×10cos(35)=16.38 .
Check: in any parallelogram the sum of the squares of the sides is equal to the sum of the squares of the diagonals: 11.472+16.382=399.8653 which is close enough to the required 400 given that we only wrote answers to four significant digits