In the diagram below, triangle ABC is isosceles, and triangle MPQ is equilateral. Find the area, in cm2, of triangle MPQ.
In the diagram below, triangle ABC is isosceles, and triangle MPQ is equilateral. Find the area, in cm2, of triangle MPQ.
BM = 36 cm
AC = BC
PC = QC
Let an F to be the foot of altitude from M to BC
∠FMP = 15°
FM = sqrt [( 36² )/2] = 25.455844
MP = FM / cos(15°) = 26.353829
PQ/2 = MP/2 = 13.1769145
The height of ΔMPQ is H = tan(60°) * (PQ/2) = 22.8230854
Area of Δ MPQ = (PQ/2) * H = 300.7378467 cm²
Since ABC is isosceles.....then angle ABC = 45°
PQ is parallel to BA
Therefore...angle QPC = angle ABC =45°
And angle MPQ = 60°
So angle MPB =180 - 45 -60 = 75°
Using the Law of Sines....we can find MP = the side of MPQ thusly
MB / sin MPB = MP /sin ABC
36 / sin (75) = MP / sin 45
36 sin 45 / [(sin (30 + 45) = MP
36 sin 45 / [ sin 45cos 30 + cos 45 sin 30] {sin 45 = cos 45 }
36sin 45 / [ sin 45 * ( √3/2 + 1/2) ] =
2 * 36 /[ √3 + 1 ] =
72 / [ √3 + 1] =
72 [ √3 -1] / [ 2 ] =
36 [√3 -1 ] = MP
So.....the area of triangle MPQ =
(1/2 ) (MP*^2 * sin (60) =
(1/2) [ 36 * [√3 - 1] ]^2 * (√3 / 2 ) ≈
300.74 units^2
Just as Dragan found !!!!!