Area of a triangle

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Given that there is a triangle A B C \triangle ABC with the lengths 7 , 11 7, 11 and 14 14 while the size of the angles are unknown.

The area of the triangle can be simplified as x y x\sqrt{y}

What is x + y x + y ?


The answer is 22.

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4 solutions

Plug the values into Heron,s Formula: A r e a = s ( s a ) ( s b ) ( s c ) Area=\sqrt{s(s-a)(s-b)(s-c)} where s = a + b + c 2 s=\frac{a+b+c}{2} So s = 7 + 11 + 14 2 = 32 2 = 16 s=\frac{7+11+14}{2}=\frac{32}{2}=16 A r e a = 16 ( 16 7 ) ( 16 11 ) ( 16 14 ) = 16 × 9 × 5 × 2 = 144 × 5 × 2 = 12 10 Area=\sqrt{16(16-7)(16-11)(16-14)}=\sqrt{16\times9\times5\times2}=\sqrt{144}\times\sqrt{5\times2}=\boxed{12\sqrt{10}} So x = 12 x=12 and y = 10 y=10 and x + y = 12 + 10 = 22 x+y=12+10=\boxed{22}

Bill Czy
Jan 11, 2014

S=(7+11+14/2) Heron's formula states that the area of a triangle is = \sqrt(S(S-a)(S-b)(S-c)) Plug in the numbers and you get \sqrt((16)(9)(5)(2))=3 4 \sqrt(5*2) =12\sqrt(10) since the area of a triangle can be expressed as the square root of y times x. x=12 y=10 x+y=22

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敬全 钟 - 7 years, 5 months ago
敬全 钟
Jan 9, 2014

By using Heron's formula, we have s = 7 + 11 + 14 2 = 16 s=\frac{7+11+14}{2}=16 , where s s is the semi perimeter of the triangle. Then, the area of the triangle would be

( 16 ) ( 16 7 ) ( 16 11 ) ( 16 14 ) \sqrt{(16)(16-7)(16-11)(16-14)}

( 2 4 ) ( 3 2 ) ( 5 ) ( 2 ) \implies\sqrt{(2^4)(3^2)(5)(2)}

2 2 × 3 10 \implies2^2\times3\sqrt{10}

12 10 \implies12\sqrt{10}

Comparing with x y x\sqrt y , we arrive x + y = 22 x+y=\boxed{22} , which is our desired answer.

your solution is 95 % 95\% same as mine

Daniel Lim - 7 years, 5 months ago

95%

Daniel Lim - 7 years, 5 months ago

By the way, area of any triangle actually also can be found by using Cosine Rule and the formula below.

T = 1 2 a b sin C T=\frac{1}{2}ab \sin C .

So, let AB=7, BC=11, AC=14. By cosine rule, we have

1 4 2 = 7 2 + 1 1 2 2 ( 7 ) ( 11 ) cos B 14^2=7^2+11^2- 2(7)(11)\cos \angle B

26 = 154 cos B 26 = 154\cos\angle B

13 77 = cos B \frac{13}{77}=\cos\angle B

B = cos 1 13 77 \angle B=\cos^{-1}\frac{13}{77}

which is approximately about 8 0 1 6 80^{\circ}16' . So, substitute the values, we arrive

T = 1 2 × 7 × 11 × sin 8 0 1 6 T=\frac{1}{2}\times7\times11\times\sin 80^{\circ}16'

T = 37.5 sin 8 0 1 6 T=37.5\sin80^{\circ}16'

T 37.95 12 10 T\approx 37.95 \approx 12\sqrt{10}

So, as you can see, the area of the triangle also can be determined by the way above. But, since we need the most accurate answer (otherwise we can't find x + y x+y ), so this way is not very encouraged.

敬全 钟 - 7 years, 5 months ago
Daniel Lim
Jan 8, 2014

By using the Heron's Formula, we can find the area by getting S = 7 + 11 + 14 2 = 16 S = \frac{7+11+14}{2} = 16

Then we get 16 × ( 16 7 ) × ( 16 11 ) × ( 16 14 ) = 1440 \sqrt{16\times(16-7)\times(16-11)\times(16-14)} = \sqrt{1440}

1440 = 144 × 10 \sqrt{1440} = \sqrt{144\times10}

Since the square root of 144 144 is 12 12 , we can simplifly it to 12 10 12\sqrt{10}

Therefore, x = 12 , y = 10 x = 12, y = 10

x + y = 12 + 10 = 22 x + y = 12 + 10 = 22

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