Formula Heron AΔ =rad(p(p-a)(p-b)(p-c)), unde a,b,c sunt laturile triunghiului si p=(a+b+c) :2 este semiperimetrul.
Aefgh = Aefh + Ahfg =2Aefh, deoarece ΔEFH =(congruent) ΔHFG
Aefh: p1= (7+8+9) : 2 = 12
p1-7=5, p1-8=4, p1-9=3
deci Aefh=rad(12x5x4x3)= 12rad5, deci avem
Aefgh=24rad5 cm^2
Aefgh= 8x9xsing=72sing, deci
24rad5 = 72sing I :24
rad5=3sing ⇒ sing=(rad5) / 3 ≈ 2,236 : 3 ≈ 0,745
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Succes in continuare!
