Answer :

frika

Answer:

C

Step-by-step explanation:

Use the Heron's formula for the area of the triangle:

[tex]A=\sqrt{p(p-a)(p-b)(p-c)},[/tex]

where a, b, c are lengths of triangle's sides and [tex]p=\dfrac{a+b+c}{2}.[/tex]

Since [tex]a=2,\ b=7,\ c=8,[/tex] then

[tex]p=\dfrac{2+7+8}{2}=8.5.[/tex]

Hence,

[tex]A=\sqrt{8.5(8.5-2)(8.5-7)(8.5-8)}=\sqrt{8.5\cdot 6.5\cdot 1.5\cdot 0.5}=\\ \\=\sqrt{41.4375}\approx 6.4\ un^2.[/tex]

Ashraf82

Answer:

Area Δ = 6.4 units² ⇒ the answer is (c)

Step-by-step explanation:

* Use the formula of the area:

∵ Area of the triangle = 1/2 (a)(b) sin(C)

∵ We have the length of the 3 sides

∴ Use cos Rule to find the angle C

∵ cos(C) = (a² + b² - c²)/2ab

∵ a = 2 , b = 7 , c = 8

∴ cos(C) = (2² + 7² - 8²)/2(2)(7) = 4 + 49 - 64/28 = -11/28

∴ m∠C = 113.1°

∴ Area Δ = (1/2)(2)(7)sin(113.1) = 6.4 units²

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